Cob Blog

One point I haven’t mentioned previously is that we got our final air test done and achieved 0.265 air changes (n50) or in terms of the q50 that BC use it was 0.31 m3/m2. Well done to our team!!

Our Passivhaus definitely does what it says on the tin. It is very warm!!

When we first moved in we had the heating on to warm it up from an average of 14.5 degrees (the builders had the doors open most days so it got a bit cold) up to around 20 degrees which it did in around 24 hours. Unfortunately, because of the momentum behind the heating this then carried on up to 23.5 degrees a day or so after the heating went off, at which point we had to open the windows. Very green!!

Once the temperature had stabilised and we’d ironed out a few control issues the heating was basically not used. Our main source of heating is now the condensing tumble drier in the basement, the dishwasher in the kitchen and three energetic children (my wife and I are too exhausted after the move to be counted as a heat source). The sun definitely contributes to the temperature inside the house but only raises it by around 1-1.5 degrees each day at the moment. Typically temperatures inside the house in the morning are around 20.5 degrees rising to 21.5 by the end of the evening with outside temperatures varying between 2 at night and 10-12 degrees during the day.

Generally the internal environment is good enough with the ventilation system running on nominal but if we are cooking then we have to put it on boost to get the cooking smells out quicker. The carbon filter in the hood works to a certain extent but largely serves to blow the smells more widely around the house. Our intention was that the two air supply ducts to the living room and the three extract ducts in the kitchen area would ensure that this didn’t happen but this has not worked out as planned. However, allowing the system to run on boost for 20 – 30 mins after cooking has finished is enough to clear the air.

There are a few unexpected bonuses, one of which is that you can leave the bi-fold door open and have some fresh air in to the house without there being a draught. I assume this is because the building is so airtight that without cross ventilation there is nowhere for the air to go. It is very relaxing to hear the birds and sheep outside without having the draught to go with it.

As we experience more of living in the house I’ll blog more of what we find but the first month has gone really well. It will be interesting to see how the house performs in the summer (should we have one this year) and whether it will over heat at all.

The end of the build is finally within sight and all being well we will be in on the 28th of March. The last few months have been informative, if nothing else, as all of the little niggly problems with all of our expensive passiv haus kit has come to light. The windows and doors have been on the whole disappointing due to poor service from both manufacturer and supplier but now issues with construction and installation quality are coming to light.

Firstly, our Solarlux Bi-folds, which are supposed to be PH approved, were not built particularly well in the factory and consequently are not very air-tight. This in itself is annoying enough given their cost but when you have to have battles with them over the phone to actually get issues rectified it does leave a sour taste. We are having new seals fitted after a whole 3 months of negligible use. Clearly a very robust design.

We have also had issues with our Internorm doors. The hinges have started to corrode on the interior of the doors which does not fill one with confidence for the rest of the metalwork in the door. This is corrosion from contact with atmospheric moisture, not rain, which makes me wonder how much one needs to pay to have a hinge that does not corrode. Apparently more than the £1700 we have paid for ours.

Having had a little rant about this on LinkedIn, several people have pointed out that you don’t need to use PH certified doors and windows. You obviously need to know what the thermal performance is and that is has been third party tested for air tightness, etc. but it doesn’t have to have been certified by the Passiv Haus Institute. This begs the question ‘Why do manufacturers get their products certified by PHI?’ as all it essentially means is that it has a sticker showing it is certified by PHI instead of any other third party testing organisation. Of course it does mean that you can charge a lot more for your windows and gullible customers (like me) pay more thinking they are getting a better product.

Finally, this is a link to our Flickr page with all the photos from the build. Hope you find it interesting. http://www.flickr.com/photos/89655652@N05/

As you can see from this month’s time lapse all the piles of rubbish have gone and we’re on to installing drains and building up for pathways and driveways. I can only hope the weather dries up a little. How much rain have we had this year?? Surely it is one of the wettest on record?

The interior is mostly skimmed out but we are still waiting for 2 doors and our bifolds from Solarlux to be installed. This means there are a few walls that connot be skimmed until these doors are in. Because of this and delays with joinery we have resigned ourselves to the fact that it’ll be a 12 month build and hopefully we’ll be in for mid February. We can’t wait!!

Once we are near to moving in we will install temperature and RH sensors in the walls and in the roof and there will also be a weather station recording hourly weather data to enable us to create a data file for Hygrothermal modelling tools to use, such as WUFI. The purpose of this is partly to test the accuracy of these tools in this type of house but more importantly, in this type of climate. We regularly get queries to the use of these systems because people don’t think they can cope with the enormous rainfall we experience in the South West. At least this way we can prove it one way or the other!!

We are very pleased to have achieved 0.25ach on our second test!! Although we achieved 0.2 on the first one there were a few areas around the external doors that we didn’t tape thoroughly prior to installing the screed in the building and so there were a few small drafts noticeable in 2 locations. I guess the moral is ‘don’t get cocky!!’, even if you think you’ve got it all covered, whenever there are any changes you need to be on top of the detailing in those new areas.

There are now lots of photos online at Flickr for people to look at. The address is http://www.flickr.com/photos/89655652@N05/

The drains are all going in now, in spite of the continuing rain. Thankfully we have good drainage on site!!

Finally the Zinc covering is finished on the roof and the walls are rendered so the interior can now begin to take shape. First fix has been completed and we are all boarded internally so we now wait for the plastering to start.

Those who have visited us are aware of the continuing saga of our windows but for those of you that haven’t – ORDER YOUR DOORS AND WINDOWS AS EARLY AS HUMANLY POSSIBLE!! We decided to use Internorm windows and doors with a Solarlux bi-fold door in the central living area. Internorm have been fine. Their distributor in the UK, not so fine. In spite of paying our deposit at the beginning of May it took 4 months for us to get the items on site and installed and even then the window sills were all wrong. Solarlux seem to have forgotten to manufacture our bi-folds too so they should finally be with us in late November. Lovely products but the 800 – 1000 miles between us can prove a barrier. I would suggest there is a large gap in the market for high quality UK manufactured fenestration that complies with Passivhaus requirements.

Once the last door is installed we can finally do our second air test. This should have been completed before the plasterboard was fixed to ensure no issues with leakage around frames but the delays have meant that this has not been possible. We can only hope that the window installation has been adequate and there are no air leaks that we cannot access, which is not unlikely. I would suggest that this is not the best way to build a Passivhaus!!

I’ve been a bit slack on posting the time-lapse videos recently so here is August and September showing the progress with the roof and some of the rendering.

In stark contrast to our hopes and expectations July was quite wet. So wet in fact that it broke quite a few records and the spirit of the guys on site!! The first half of this month’s time lapse was unfortunately blighted by our leaky camera but I bought a new one half way through. If you stick with it a little you can see all of the rafters going up on the South elevation of the roof and then, after switching locations, you can see the boards and counter-battens, etc. going on to the South roof.

The house had it’s first air test this month and vindicated all of the time and money we have put in to making sure it was air tight. The building has an internal volume of around 1160 cubic metres and around 1100 square metres of surface area. We achieved a n50 of 0.23 ach and a q50 of 0.24 m3/m2 which is a fantastic result for all concerned, especially as we had spent several days just designing how we would make the building airtight.

The build-up of the roof, just in case you were wondering, is 300mm of UdiFLEX flexible wood fibre insulation in between the rafters, 100mm UdiTHERM wood fibre board on top of the rafters with UdiTOP wood fibre sarking board over this. This then has 25mm counter battens over, to allow ventilation, with 18mm OSB and breathe membrane over to support the zinc roofing that will finish it off.

We are now dry inside at least and the first fix of all of the services are currently going in. We may even get our Internorm windows eventually, although I’m not holding my breath!!

Finally the walls are up and the roof is almost on and it looks amazing!! The curve in the building is now really evident and adds lots of interest. Annoyingly, all this has happened through the wettest second quarter since records began. The frame had been manufactured several months prior to erection and had been carefully stored in a large, dry shed to ensure that the OSB, our air tightness layer, was perfect for it’s arrival to site. Within 48 hours of the frame being up it was all soaked. Anyone who knows anything about OSB and air tightness knows how bad that is!!

The walls all went up in 2 days (albeit 2 non-consecutive days because of the foul weather) and the idea of splitting the spine wall of the house in to upper and lower panels has worked perfectly for connecting the air tightness layer on the North side of the roof to the South slope. The 300mm joists for the roof were placed manually (in the rain of course) so we are hugely grateful to Tribus for persevering in spite of it all.

Currently, the North roof slope is complete except for the Zinc outer layer and the South slope has all of the rafters on and will shortly be insulated and covered. Then, finally, we will be dry inside and the speed of progress can increase irrespective of the glorious summer (somewhere it is a glorious summer, just not in Devon).

Last week we had the office air tightness checked by Steve Simmonds at Watergate Services as a guide to the effectiveness of our air tightness plan. The result was fantastic!! We achieved 0.63 air changes per hour (n50 = 0.63ach) and a q50 of 0.44 which complies with the Passiv Haus requirements. Given that there were a few areas leaking and that I’d forgotten to put grommets around some of the service ducts entering the office, that was a fantastic result for a first attempt.

We used the UdiSTEAM Elastoflex tapes throughout the office and the house for sealing all the OSB joints and from the OSB to the floor. Where we have internal partitions meeting the outer walls and roof UdiSTEAM Butyl tape was used as this is better at sealing nail holes. We should see in the next few weeks how our strategy on the main house has worked!!

Finally, we have just started our series of site visits/seminars which will cover the various stages of the build, how the house is built and the rationale behind many of the design choices. There are still a few spaces left on the first set of visits, please contact us if you’d like to visit.

Here’s what happened this month a little speeded up!!

The ground floor is now built and the building’s shape is becoming apparent. It was designed to have a facetted curve in it so don’t think that it was just built badly!!

The floor construction is again 200mm of reinforced concrete on 300mm of Isoquick polystyrene flooring creating an insulated floating slab as has been built for the office and the basement floors. The whole system does go together very well although it is quite awkward when joining sections together which aren’t standard angles. Once again, the builder is very impressed with the Isoquick system.

Now that the floor has been built it has highlighted the negative side of building an insulated slab. The ground conditions at the western end of the building were ideal in that the soil was very stoney so not much stone was required to build up under the slab. However, conditions at the eastern end were very much less favourable and required enormous amounts of stone to build-up under the slab. All in all 47 loads of stone have been brought in to infill around the basement and build up under the building to the correct level. This is not so sustainable!!

Where ground conditions are good/favourable and insulated floating slab is perfect, however, more engineered solutions such as concrete lattices, should be sought when the ground is poor. We’ll know for next time!!

The next job was to ensure that the whole base was airtight which involved a great deal of thought around the junction from the basement to the floor slab and then also around creating an airtight layer that could connect to the bottom of the frame. We’ve assumed that the radon barrier/DPM will act as an air tight layer and have connected that to the poured concrete walls of the basement and also back in to the surface of the whole floor slab internally. This has involved an awful lot of double sided tape and membrane but we think we’ve got it cracked. In the mean time the office building is being tested for airtightness to ensure that the methodology we are employing works.

The timber frame is currently under construction although the rain and strong winds are stopping the erectors getting on. Apparently we are back in February again!! Also, sorry about the misty bits in the video, our outdoor camera kept filling up with water, apparently they don’t have Devon monsoon rain where the cameras are normally used.

The basement construction has gone well so far and is now complete. The walls are tanked, the concrete planks for the floor are on and the guys on site are filling in around the basement with stone as I write this.

The basement floor went in well although was rather complicated by the seemingly excessive amount of steel reinforcement that was apparently needed. The same theme carried on up through the Logixx ICF that we’ve used for the basement walls and made progress a little slow. However, the pouring of the concrete into the system went very well and very fast. The system was very stable, there was no movement during the pour and all involved are very happy with it. Even the builder on site thought it was ‘Lovely!!’, although strictly I am forbidden to write that in case anyone thinks he enjoyed the experience!!

The Logixx system is not the cheapest on the market but having spoken to other contractors and having seen our contractor install it for the first time, I too would have to suggest that it is a fantastic system. Given that there is 2.5m of concrete in it and none of it leaked out anywhere, it is very robust. My only criticism is that there needs to be a little more joined up thinking from structural engineers working with it as the steelwork design made progress unnecessarily slow at times.

The concrete planks went on to the basement shortly after the ICF was finished and also the concrete stairs into the basement. Even though I’m not necessarily a fan of concrete, I have to say they are objects of beauty. The finishes on both the planks and the stairs is perfect. Well done Page Concrete. Also well done to their lorry driver who managed to drive through a wet field and into our site with a fully laden articulated lorry. He even managed to get it back out again!!

We are now on to the ground floor slab and also trying to work out how we best attach the airtightness membranes to the top of the basement walls. The next month will be exciting for us as we finally see the footprint of the house emerge and also watch the timber frame go up.

Finally, slight apology on this month’s video, I forgot to take out the Easter holidays out of it so there are a few days where the only activity is from sheep walking by in the field next door!!