andeebee

I still have the nightmare of the extension to house interface to deal with, have been waiting for the existing house wall and roof to be made good before attempting. This involves roof trusses and floor joists sitting on the wall plate which leads into the depths of a (well) ventilated loft, not helped by sub floor ventilation from open ended floor joists into loft space (Americans call 'Cape Cod' style house) No consideration for bagging the pozijoists was made, until I suggested it (following installation, whilst staring up at the mess). If I can isolate the new extension from the house, I hope to recoup some of my spend on insulation on the extension, otherwise it will be blowing out the other side of the house The stress this is causing is huge, nobody seems to understand the problems I am seeing and how to deal with them. All design problems, that should have been considered up front. How many architects wander round a site during a build thinking 'that doesnt look good, how could I make that better next time...?'

Thanks to all the above comments. I have spent the last few weeks trying to fill the gaps left by the bad fitting warm roof, using PIR cut up into blocks and foaming them in I used a airtight foam on the inside perimeter and a large area 'coverage' based foam on the outside. Still not sure I have got all the gaps, due to the now inaccessible cavities between the outriggers and the roof edge Had many sleepless nights adding up all the area of the blocks I have cut, to literally cover the daylight coming in. Had this not been addressed, at least partially by my efforts, it would have been like leaving a window open continuously. I think the best way to have installed this would have been to fill the gaps between the outriggers, prior to the installation of the roof section, as you would have far more access. The roof could have then been built onto a continuous layer

Before my refurb, I used insulation 'batts' on the vertical sections. If you can buy close to the width of the vertical cavities this saves you having to cut up on site/in the crawl space. I then fit a second layer going in the opposite direction and then wrap the lot in a windtight fabic as suggested above, to prevent wind wash Also consider the exposed loft floor in the crawl space also appears uninsulated , so I would use standard fibreglass insulation here to around 300mm to keep the rooms below warm

My 1960's dormer bungalow is also incredibly cold in the winter which is worse when the wind is blowing Having recently removed the skirting in all the ground floor rooms, I found gaps you could fit your hand in, straight into the ventilated sub floor The sub floor timbers were in perfect condition! I would check your rooms for air leakage points, as I imagine, like mine , some of your heated air is being drawn through the house and into the sub floor Beyond that, but more intrusive, is insulating below the floorboards as others have mentioned

The gaps around the outriggers are due to added packing required to bring the roof deck level due to the discrepancy from the interface with existing building

More images...

I am mid way through an extension and house refurb The extension is a timber frame using a warm roof on pozi joists and I am increasingly worried about the separation of the roof insulation layer from the conditioned space below due to the difficulty in sealing up the gaps between the pj and the top layer of the walls with PIR To further compound the problems, I wanted an overhang around the extension. Whilst the PJ's facilitate this structure naturally on the one face, the two sides are forming the overhang using outriggers Combine the outriggers, packing and the roof fall angle and you can currently fly a drone through some of the gaps between the roof deck and the walls Whilst air tightness could be achieved using a vcl, heat loss from the break in insulation continuation cannot and I don't understand how we have got here Possible solutions I have considered are commercial spray foam sealing from the outside of the roof cassette and the inside or my latest idea to fill the area below the roof deck with blown in insulation. Please share your thoughts and possible solutions

Thanks both, sorry I missed the bit about removing the ceiling and fitting the insulation that way. Of course makes sense and less disruption.

Yes, you are right, my fears about using EPS are confirmed then. I think a better option, albeit more invasive, would be to lift the floor in the bedroom and fill the void with fibreglass. The joists are 150mm so I can fit a good layer in there. This was on my plans but as its so disruptive wouldnt be a job I could do over a weekend as it requires complete bedroom teardown

I was hoping to get a good layer of maybe 200mm as I have loads of head room in the garage, but you are right the air gap above will probably negate this.

Im currently insulating the house (large dormer bungalow) from the inside, using mainly glass fibre and rockwool. The rooms are room in roof design with a knee wall. The upstairs master bedroom is above the small garage and I discovered today, whilst foam blocking the subfloor cavity under the bedroom floor, that the plasterboard garage ceiling is separated only by an air gap before the flooring of the bedroom above. Blown in cellulose would fill in this void perfectly, however this would not be viable for such a small area. This led me to thinking maybe I could insulate from the garage side. EPS foam is light and could be mechanically fixed to the upstairs floor joists, through the existing plasterboard. Using a good depth of EPS would serve as a great insulator to the room above, however Im aware of the associated fire risk. Would using a fibre cement panel lower this fire risk, or should I look for another method to insulate this area?

Having broken out the thermal camera, during the recent storms, I was shocked to find some internal walls getting as low as 5'C. The worst side of the house is a long flat roofed dormer, housing two bedrooms and a bathroom. I found a hardboard panel inside our bedroom cupboard and removed it to find an impromptu access hatch to the dormer and roof 'triangle' cavity. Some plumber or sparky must have been in there a long time ago. This North side of the house is the coldest and the wind is whistling through the cavity, suggesting any insulation present is suffering from wind wash. My first thoughts were to employ some air tightness measures to reduce the wind, but am I better focusing on insulating and adding a membrane to the living area side of the cavity and leaving the roof side free? Existing loft insulation is poor and will be renewed however while Im in there should I add a membrane across the ceiling, draped over the insulation, to prevent further heat loss? There is also the cavity under the bedroom floor to block - should I just foam in some PIR cut to size, to block the wind going through? Insulation wise, would cavity batts be the best choice for the vertical stud walls? Currently some thin, 25mm, glass fibre is resting there (in places)

Similar to above post, I put alot of work into making good our new build (Taylor Wimpey) as we had similar problems in a upstairs bedroom. Using a thermal camera image it showed the roof joists, similar to the images posted. The loft insulation was very badly thrown in and needed completely reseating. I also foam filled the ceiling joist closest to the external wall as this was a 30mm uninsulated gap. This ran from one side of the house to the other. Rather than poke insulation into the gap, I opted to fill it with foam, using a foam gun, that way I could air seal the edge of the ceiling plasterboard at the same time. I also measured the loft insulation as I was under the impression it should have been 270mm for regs. I think it was under 150mm. When queried, the site foreman promptly sent round the loft insulation people and another layer was thrown in. Once rearranged and laid in right angles to the existing rolls of insulation, the house heat loss was much less. Thermal imaging in the same area confirmed the work was good. Worth checking if you have cavity closers fitted as you could be getting windwash up through the cavity. That condensation needs to be addressed and shows the air leaks you have from the conditioned living space below into the loft, taking with it warm, moist air which is condensing on the cold fabric and roof joists. Will soon turn to mould and eventually rot. Check the loft hatch closes against a seal and the hatch frame is seated flush to the ceiling. The hatch is a huge opening and should be addressed first. Also check any ventilation from bathrooms/showers upstairs are vented outside. All of my ventilation hoses had been covered with insulation and flattened! Since moved from the new build to a cold older house and starting the insulation journey once more. Good luck with your investigation and do not believe a word the house-builders say - always fact check.

Just noticed, on page 20, in the downloadable guide that Ecological Building Systems provide for implementing this system, they advise the use of wood fibre cladding under the joists. This would provide the windtight and breathable layer whilst reducing the cold bridge into the floor joists and negating the need for the lower Pro Clima membrane. Would imagine they would be a pig to fit though...

Ah, thank you SparrowHawk. I missed your post, possibly due to the use of PIR as I intend to use woodfibre. I have had a read through and there is some good info on there to digest. The top of joist topic is one I hadnt considered, but was aware this thermal bridge will remain, regardless of the U value between the joists. Did you find a solution to that?