First airtightness test

Tomorrow (5th April) is a big day for the project. Paul Jennings from ALDAS, will be conducting our first airtightness test. We have been preparing for the day by going through the whole building to ensure there are no forgotten gaps or holes.

All the windows are now in and although there are still snags and issues to be resolved, they all close well enough for the airtightness test. In the refurbished part of the house, the windows are mounted on the ouside of the original walls with the external insulation wrapping around the window frames to minimise the thermal bridging around the window edge. This also minimises the area of window frame, which helps aesthetically and improves the energy performance of the window installation because window frames are generally the poorest performing part of the window. The photo below shows a section of a window with the first of four layers of insulation attached around it.

The next photo shows another section of window with all 180mm of phenolic foam in place. The work to cut and attach the insulation was time-consuming and really unpleasant for the team -  the stuff makes you really itchy. The job was made more difficult because Kingspan would not supply their product in broad sheets of 100mm and 80mm depths. Instead we had thinner (40mm and 50mm) and smaller area sheets. This meant much more glueing and cutting. We have also had to use more of the fixings than would have been needed with the broader sheets. Thank you Kingspan.

In the photo below, the airtightness tape is being applied to along the base of the window, forming a seal between the window frame and the previously parged internal window reveal. We probably have not approached this very well, as the process took longer than expected and was very fiddly. Because the parge layer was rougher than is ideal, we felt we needed to use an adhesive primer in addition to the Tescon Profil tape. It was hard to control what then becomes a very sticky combination of materials! We will need to check back with suppliers, Ecological Building Systems, to try to do it better next time.

We have two large service penetrations into the roof: for the soil vent pipe (SVP) and for the flue. We are using a small gas boiler, which modulates down to about 4kW, to provide our winter hot water - solar thermal will deliver the rest - and any residual heating we may need in the coldest weather. As well as an airtightness issue, SVPs and flues create a potential thermal bridges. The flue has a pair of concentric pipes, the inner one to vent exhaust gases and an outer ring to take in air to the boiler for the combustion process. The flue runs through a grommit/Intello, past 350mm of Warmcel, 22mm of Steico wood fibre board and through the Solitex roof underlay. It could therefore, unless insulated around the pipe within the house, be a significant thermal bridge. We are planning to enclose it, and the SVP, which presents similar issues, with sheep's wool insulation within the boxing. The lack of a need for a flue in an electricity based heating system, i.e. a heat pump, makes gas a less attractive option in a Passivhaus. However, I must admit that the extra cost of a heat pump based solution put me off a bit when we were at the design stage. The Passivhaus Institute are keen to encourage manufacturers to develop and sell "compact units". These have about the same footprint as a fridge freezer - so are super space efficient - and combine the MVHR, hot water (DHW) and space heat product functions in a single unit. One, the Compact P made by Danish manufacturer Nilan, has been Certified by the Passivhaus Institute, and is being promoted in the UK. It looks quite promising, however, most combined devices don't deliver the same performance as the "separates" units would. Our MVHR unit is almost twice as electrically efficient as the Nilan Compact P. And I think compact units need to be completely modular in design, so that parts that fail can be replaced independently of the rest of the machine. The other argument in favour of using heat pumps for DHW and space heating is that they will be better in climate/CO2 terms than gas, as the renewables portion of the electricity grid mix grows. I think that in another five or ten years, the balance - and the economics - may well have shifted in favour of heat pumps and I hope compact units.

 
We also have two large penetrations for the heat recovery ventilation (MVHR) unit's intake and exhaust ducts. The ducts themselves are 160mm but are wrapped in 125mm of insulation, making the penetrations 410mm each! This photo is from the inside, where the ducts meet the airtightness barrier, which in this part of the building is the internal plasterwork (parge coat). The walls are still to have their finishing layers of plaster, which will encase the grommit, intello and tescon tape. The continuation of the ducts will also have 125mm of insulation right up to the insulated surround of the MVHR unit.

Week 4 ends

Windows finally ordered on Wednesday. I managed to get the window spec selectively trimmed using PHPP to test what effect this would have on the building's performance. The PHPP paid for itself many times over just in this one week of 'optimising' the spec.

Getting to grips with Therm (also after a long struggle). The model of the external floor-wall junction I created, has produced a provisional psi value of 0.15W/mK, lower than the 0.2W/mK estimate I had previously. Putting that more accurate figure has trimmed another 0.5kWh/m2.a off our Annual Heat Demand. Helpful, as it allowed me to trim a bit more off the window spec.

I have a sense of having achieved quite a bit this week.

Meanwhile, the scaffolders have been busy by this time next week, the whole house will be shrouded in a tarp and tin weather shield that will protect the existing structure from the rain and provide a working environment for the site operatives more conducive to accurate and quality work. It also much reduces the risk of weather-related project delays. We have been lucky in that we have missed most of the bad weather affecting the rest of the country, although night time temps have dropped to as low as -10C. Even though we have not had much snow, it has not been nice weather to be working outdoors.

Week 4 begins ... the latest on windows and on thermal bridges

Windows

Week 4 starts and we Still Haven't Placed Our Window Order. The process of placing the order is taking a lot longer than I'd anticipated. I am optimistic that we will be in a position tomorrow, finally, to press the Go button.

This has all come as surprise to me, as I'd thought naively that we could spend time fine tuning our window spec, then present our carefully worked out window schedule to our helpful, local Internorm distributor who would then be able to process it quickly and simply ... no probs, job done.

I realise now that we should have sat down and gone through our schedule with the distributor and talked prices and options at least two months ago, despite not having planning permission or completely finalised window dimensions at that stage. The order process is slow because, while it is easy to spec out the windows for their required energy performance, there are so many other variables to consider and requirements to fulfil. One is the thickness of each pane of glass. If the glazed unit is over a certain area, 4mm glass has to become 6mm. For a given width of bead, this means 4mm less space between the panes, which has a significant impact on the U-value of the glazing. None of these are problems in themselves but overcoming them adds to the cost of the windows unnecessarily.

Better to use slightly less exacting window performance figures in the PHPP. That way, you can order standard products and get a much more cost effective solution. It seems obvious to me now that I am writing this and, in fact, I have used been using conservative figures throughout the PHPP but I think I got carried away by all the exciting "Leading Edge" or best case figures that the different window manufacturers banded about. Assuming your chosen window provider is in the business of manufacturing windows with near Passivhaus performance, the conversation needs to be about what their standard spec is on those windows. It also needs to be about whether window sizes or other variables will make it harder to achieve the energy performance you are planning for in the PHPP.

Here are my rules of thumb:

	My "Leading Edge" Spec Assumptions this time	More conservative PHPP assumptions I will use next time
Glazing "g"-value	0.6 or 60%	0.5 or 50%
Glazing U-value	0.5W/m2K	0.6 or even 0.7W/m2K
Frame U-value	0.94W/m2K	0.94W/m2K
Spacer psi-value	0.038W/mK	0.05 or even 0.1W/mK

I got it right with the frame U-value, because I knew that the "leading edge" spec was a lot more expensive than their standard Passivhaus spec.

These figures aren't set in stone and I'm sure that each year what is considered standard "Passivhaus suitable" spec will improve.

Thermal bridging

On Thursday, I attended a one day course on how to use Therm, together with a very helpful Excel spreadsheet developed by Peter Warm, to calculate the psi-values of thermally bridged building junctions.

Therm is not at all intuitive but does have the advantage of being the only free software that can be used to derive a psi value for many types of thermal bridge. Therm can only model in two dimensions and more complex (and very costly) software needed to model certain types of thermal bridge junctions.

I have been grappling with this for some months but am now finally biting the bullet and getting to grips with Therm, so that we can replace the conservative (I hope) thermal bridge psi-values (0.2W/mK) we have used in the PHPP to quantify the additional heat loss through the floor-wall junctions of the existing house: this type of thermal bridge is unavoidable in a refurb but can be designed out in a new build.

Likewise, I want to model the junction between the existing house walls and the window jambs (sides), heads (top) and cills.

Meanwhile, the first insulation is being installed around the base of the walls of the existing building and in the base of the new build side extension.


We had to buy double quantities of the insulation in half thicknesses because, even though the thicker sizes do exist, the suppliers will only sell them in very large quantities, unsuitable for a project of our scale. I asked our builders to stagger them slightly to reduce possible thermal bridging in the inevitable, if tiny, gaps between each piece. So instead of this...

As we got around the corner, we started adding a 50mm overlap, like this...

It means a little bit of extra labour but it is essentially a free way to get the best from the insulation you are using. The images above are of the insulation around the base of the existing building, 2 x 60mm thick, which we are fitting from DPC level down about 400mm.

Installing dual layer of Foam Glas, under the toe of the concrete slab, where the weight of the walls of the new build will bear down - Foam Glas can take much heavier loads than other insulation  - we are also taking the opportunity of staggering the two layers to minimise unnecessary thermal bridging.

Later this week, the scaffolders will be here to start setting up the shroud that will cover the building for the next three months while the external wall insulation, the windows and the new roof are put in place.

Week 1 of the build

We started on site this week after a rapid exit into temporary accommodation following long awaited granting of planning permission. I was determined that we would not delay the project, before the build had even started, by failing to move out in time. We only just made it though!

The construction team got to work with great alacrity and a building that had been our home three days before very quickly became a building site. All of the wooden stud partition walls are gone, as is all the internal plaster work, which practically came off on its own. Also gone are all the ceilings, all electrical cabling and sockets and all the old kitchen and bathroom fittings. One of the builders found someone to take all of the pine flooring, which he is going to de-nail, re-sand and lay for a small new build in the neighbouring county. Given that it was installed second hand in our house, it will now be getting its third use, which is very satisfying. Still, despite the fact that nearly all the existing structure remains, five or more skips have been filled so far, although the skip company will sort all the contents to separate out any recyclable material.

The attached garage, which is going to be replaced by a single storey new build, is also gone, except for its concrete floor, which goes next week, together with all the windows. Next week also sees the end of the road for the hideous concrete chimney, an original feature I'm told: I really can't imagine what possessed the architect or builder who specified it back in 1970.

It is interesting seeing the building reveal its structure. The quality of the original workmanship is no longer hidden. The 70mm of underfloor screed was removed today to allow us to insulate the floor with the minimum of increase in finished floor height. Unfortunately, the ceiling heights are not especially generous and we could not simply add the insulation on top of the existing screed. The original concrete slab is now exposed everywhere and, as expected, it is very rough and uneven and we will need to find a way to create a level, even base to place the insulation onto. As I think I discussed in an earlier post, the floor was one of the hardest-to-treat elements in the design stage. We were not able to design a floor with a U-value of below 0.15W/m2K, not without spending silly money on very exotic forms of insulation. We have managed to compensate for the relatively poor (>0.25W/m2K) floor U-value but it is still essential we get 70 to 80mm of insulation in there to get the building through Passivhaus Certification.

This week, we have been going through the fiddly process of building up an order for the Internorm windows. We must finalise the order in the next 12 days to avoid risking delaying the project. I had promised myself that we would not cut things so fine with the timing of the window order but this is proving quite hard to achieve. I can see how easy it is to delay progress on a build by taking your eyes off the windows.

One of our windows consists of a large, undivided, fixed, north-facing, triple glazed unit. If there are no other constraints, it is apparently possible to get a U-value for the glazing (Ug) of 0.5W/m2K without using very rare and expensive Krypton gas. Because UK building regulations require 6mm glass for (for inner and outer panes?) in windows of greater than 1300mm height (?), rather than the usual 4mm glass, we lose precious mm of Argon-filled space between the panes. This constraint means that the glazing can only get a Ug of 0.6W/m2K if we stick with Argon. The PHPP will come into its own again when I use it to check whether de-rating this window's glazing to 0.6 will affect the building's overall performance significantly. It is worth doing, as adding Krypton into this one window adds a few hundred pounds (£££) to its price.

It has been interesting as the builder works on further rationalising some of our design choices: balancing materials cost (financially and environmentally) with labour costs and simplifying the execution to minimise the risk of error that could create unintended thermal bridging or air tightness issues. We have managed to simplify a couple of the building junction details. As a client, it adds fantastic value to the project to have that second design iteration. However, it is only working because of the excellent communication and mutual respect between builder and architect. The importance of this team working, "common purpose" if you like, between architect, builder and of course client, has been underlined for me again this week.

Windows revisited

We have made a few changes to the windows.

We decided to use Internorm some months back for various reasons discussed in a previous post. We had planned to use their "Varion" triple glazed range in the north and south windows and Varion 4 range - with triple glazing and a fourth pane that encloses integral, external blinds - in the east and west windows, of which we have too many; this is to compensate for constraints on the south side of the site. An ideal Passivhaus has lots of south facing windows - ca. 25% of the south façade area; modest amounts on east and west façades and minimal window area on the north façade. There's more on our east west windows and the Varion 4 dilemma further down this post. First, something about skylights...

Internorm do not make skylight windows and so we looked at Velux and Fakro, who do. We had planned a large Velux window that the top of the south facing side of the roof. But this window has now been ditched. It would have added more light in our stairwell but we are already improving the daylighting dramatically, so the extra provided by the Velux didn't seem essential. We had also thought it would provide nice stack-effect cooling in summer, being at the top of the house. We (I) have been put off by Velux's poor communication, their incomplete technical data and by a lack of confidence that we would be able to detail and execute the installation well enough. In the PHPP, a Velux would only have brought a net benefit in winter solar gain if the window spec and installation had been good enough. Putting in conservative estimates into the PHPP (in lieu of verifiable data) for the Velux window/installation resulted in no net benefit in heat gain from the window - the additional losses resulting from installing the Velux roughly balanced the solar gains through the window. The window we were looking at was one aimed at the Passivhaus market, although they don't market it in the UK. Trying to get the key information needed for the PHPP from window manufacturers seems to be quite hard. The U-values for the frame and the psi-values (the linear equivalent of U-values) for the spacers (the bits that hold the panes apart around the edge of the sealed double/triple glazed units) seem always to have eluded us! These two factors have a significant impact on the whole window's performance and tend to be the poorest performing parts of a window. Also, it wasn't clear whether the window had a single or a double, all round gasket - the latter being essential for reliable, durable airtightness in an openable window or door. Velux's figure for the "g-value" of the triple glazed unit was not great either, 0.46, meaning that only 46% of the sun's heat energy is let through the glass. 0.50 is the minimum for a Passivhaus; 0.60 or higher is worth aiming for.

The other manufacturer that makes a triple glazed skylight-style window is Fakro. I didn't investigate their products in as much detail as the Velux because, by that stage, the whole idea of a skylight in our project was beginning to look less appealing. The other issue with a south facing skylight high up in a stairwell is that you need an electrically powered and electronically controlled mechanism to open and close the window and its external shuttering. Without these, the window would be a source of summer over-heating. With them comes over complexity and problems if (when?) the mechanism fails.


Back to the east west windows. On a visit to Internorm's shiny new showroom last week, we learned that the only way we could get Varion 4 triple glazed with a fourth pane for integral, external blinds, was to use krypton gas, instead of much cheaper, more abundant but less highly performing argon to fill the sealed units; this is due to space constraints. You can make krypton units much slimmer for the same performance and their main market is in listed buildings, where a high performance double glazed unit can be designed to look like a traditional single glazed window. The external blinds are important to keep overheating well below the modest Passivhaus target of less than 10% of days annually where internal temperatures rise above 25C. If we had been able to have less east-west glazing, we could have managed with the standard Varion windows and more ad hoc shading arrangements. The other problem with a total of four panes, is that our g-value for the window would have been less favourable than with the standard triple glazed Varion windows.

It is possible to fit shutters or non-integral external blinds but using these created other difficulties because of other constraints arising from this being a refurb project.

So now, we have decided to go for the double glazed Varion 4 windows with a third pane to enclose the integral blinds for most of the east west windows. It seems that, although they are not true triple glazed units, the third pane provides a measure of additional insulation, a bit like secondary glazing can do, with the U-value coming in at around 0.9 to 0.95.

Putting these windows into the PHPP did have a small effect on the annual heat load. The last concern was about the temperature on the interior surface of the window. One of the key principles of Passivhaus design is to ensure that no interior surface has a temperature more than 4C lower than the ambient temperature - a bigger temperature gradient reduces thermal comfort and risks creating draughts. Using a U-value of 0.95 and a worst case scenario of a winter night of -10C gives you a temperature of 16.3C in the calculation below, still just warm enough.
In practice, I am sure that these windows will be fine and even though they appear to be ok, just, Passivhaus wise, I suspect that it may make certification more problematic. Watch this space!

p.s. Have just realised that it is possible to insert pictures anywhere in the text and to insert more than one per post, so will definitely use more in future.

January update

I have not written anything on the blog for few weeks now. This has not been due to lack of activity!

We are working on the design. I don't see it as a problem that we are taking plenty of time to get the design right. It is much cheaper to change things at this early stage! The architect pointed out another thermal bridge problem that I'd failed to notice before. Part of the building, currently a garage, is attached to the neighbouring house. We need to re-look at our solution to eliminate a significant thermal bridge at the corner with the neighbour. I also want to minimise any party wall issues if possible, as I've never met the owner; he lives 12,000 miles away.

I am also starting to enter data into the PHPP - Passivhaus Planning Package - the huge Excel-spreadsheet based tool used to model proposed Passivhaus developments. The data entered, and any assumptions made, all need to checked very carefully. It is very easy to overlook something that will give you an over optimistic picture of how the house will perform. It is vital to use the tool during the design phase, as correcting problems that it flags up, like the potential thermal bridge I missed above, is often very difficult and expensive.

We have chosen our favoured window provider. Unfortunately, there are no manufacturers of Passivhaus Institute accredited windows in the UK. Until the Passivhaus market grows, this is unlikely to change. Using windows with the PHI accreditation is important because it means that technical performance of the windows has been independently scrutinised and tested. It gives confidence to Passivhaus builders that the windows will do what they say they do on the tin.

[Edit on 23/Jan/10 - there does appear to be one UK manufacturer, Greenspec, who produce a range known as "ecopassiv", that claims a whole window U-value of 0.75, which would be low enough to meet the Passivhaus standard. They do not appear to have certification from the Passivhaus Institute but do meet the AECB Carbonlite Gold Standard. There is more information here: http://www.greenspec.co.uk/html/product-pages/ecocladwindow.php - click on the product brochure for the ecopassiv range.]

Because we are forced by the constraints of the existing building to have quite a lot of east and west facing glazing - not ideal because unshaded east/west windows cause summertime overheating - we wanted a window with integrated external Venetian blinds. This will allow us to keep the daytime heat out without plunging the room into darkness. I also much prefer "tilt-and-turn" windows that open inwards and can be operated with one hand. They are so practical in many ways; once you have lived with them, any other type of window seems unsatisfactory.

The other vital task now is choosing our builder and deciding how we are going to work. A very formal arrangement of tendering, backed up by copious documentation, will not give us the flexibility and the type of working relationships we need. It is very easy to get focussed on the hardware of a Passivhaus, and on modelling it in the PHPP, but one of the most important decisions in the project is choosing your two key partners - the architect and the builder - building a trio that co-operates well as a team. This is, of course, very important in all builds but especially so in a Passivhaus where there is very little room for winging-it with last-minute workarounds to correct mistakes. In Britain I think we are great at winging it and less good at following a proscribed methodology. I am no exception to this. And both approaches have their pros and cons of course. The other vital ingredient is very good communication between the trio of client, architect and builder, with all of us checking that the others have the same understanding of how to proceed. It also means all parties have to be be engaged, really to want to achieve the Passivhaus standard. I'll write more about this later I'm sure.

Designing the layout and choosing windows

I haven't posted for a while but the project has been continuing. We have been busy working with our architect to design the internal layout of the house; focussing on stuff that clients have to consider in the design stage of every such project. We are trying to make the best use of the space for our current and expected future needs and, to a lesser extent, for the needs of a potential future buyer - although we are not planning to sell for many years. One point to consider during the design of the layout is how to minimise the hot water runs from the hot water tank or thermal store and the various point of use.

At this early stage in the project, it is so easy to add to our original requirements, so-called project scope creep. So far, I've added a smallish (3.5m x 9.7m) green or living roof on what would have been a plain, flat roof! Nothing to do with Passivhaus but it will give us a bit more green space and a nice view from two of our bedrooms. It should also help to moderate temperatures in the summer.

We have not yet specified exact window sizes, just their approximate positions, which will often be where the existing windows are located. I am also looking at window and door manufacturers. This is easier in one respect in a Passivhaus project because there are relatively few products that have been certified by the Passivhaus Institute as meeting the necessary performance standard. The U-value of the whole window, i.e. the glazing and the frame, must be 0.8W/m2K or lower. Most new windows in the UK are in the range 1.5 to 2 and are double glazed. Passivhaus certified windows are always triple-glazed but triple glazing alone is not enough to reach the PH standard. The design of the frames and the spacers (the bit between each pane in the window). Frames and spacers must not create any thermal bridging between inside and outside. Triple-glazing has three properties relevant to Passivhaus: a very low U-value for the glazed area, an inner surface temperature within two or three C of room temperature (in winter), this helps with thermal comfort; lastly, triple glazing lets less sunlight through than their double glazed equivalents. The best Passivhaus windows try to address this last point by using glass that has the highest "G-value" - a measure of solar transmittance. Passivhaus windows are also designed to ensure that the 0.6 air changes per hour standard is not compromised. They have multiple seals to ensure this.

Even if you find your 'perfect' Passivhaus window, their real world performance will be determined by how well they are installed. Passivhaus window manufacturers are based in the countries where there is a significant PH market and only the larger ones have a UK presence. Two of these are Internorm and Nordan. Internorm have an agent for our part of the country and their installation teams have been trained in a two day course by Internorm. However, I doubt that their installation teams have ever installed windows for a Passivhaus project, where airtightness and avoidance of thermal bridging are both so important.