andeebee

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?

Yes, I will be trying to follow their example as closely as possible, using the upper DA membrane. Im not opposed to using the materials stated, Im just conscious they are a merchant selling those products and in a world where I had a bit more cash, I would probably tick the boxes and get it all delivered. Just wondering if I could save a few £'s by using other materials

Throwing away all my desires and plans for going fully UFH with a solid, insulated sub floor in my 1960's dormer, due to proposed builder quotes, I have reverted back to plan B, which was to insulate between the joists and stick with radiators in the rooms. Following the great guide on the subject on Ecological Building Systems website, my question is is it really necessary to use Pro Clima Solitex Plus as quoted, or could I get away with another, cheaper material in this layer - like some of the better roofing membranes that are available? I would anticipate the membrane would not have to handle a great deal of moisture moving from the insulation to the ventilated space and act primarily as a windtight layer. I have no doubt the Pro Clima is good stuff, but is also expensive when compared to good old Tyvek roofing membrane, which also comes in larger sheets, so less taping Any thoughts or experience in this area?