Hi all, I'm planning to install Celotex inside and to underside of rafters to 0.17Uvalue. Currently I have insulation at ceiling level and eaves vented with 5x 90mm circular vents each side of an 8.5m house (15k m2/m). Ideally I would leave a 50mm gap between sarking and celotex and ideally I would upgrade my eaves and ridge to 25kmm2/m and 5kmm2/m respectively as per uk building regs.
However a roofer has told me that I would need scaffolding to install these and this makes the vent upgrade job somewhat expensive (he was saying £800 for scaffolding £250 for parts and (I guess) a couple of days making the total close to £2k. I'm going to get some more quotes but the scaffolding does add a lot.
So, I'm looking for sensible alternatives but I do definitely still want to do the pitch roof insulation if possible (downlighters, wiring, future maintenance, storage etc).
He suggested to only add a load of additional circular vents to underside of the eaves (as they would be easy to add from a ladder) - lets assume 25km2/m and he was suggesting that this would (probably) provide sufficient airflow across to prevent structural issues. He also suggested if I put insulation under rafters (not between) then the gap would be bigger and would allow this airflow more easily.
Also I have 75mm noggins supporting gable straps in between the last 3 rafter each side (12 straps in total). This will reduce the gap to 20mm (rafters 95mm). I could drill a few 25mm holes in the bottom.
My questions if anyone has got this far!
1. Would this eaves-only venting approach likely to cause damp/structural problems (a) with 50mm gap (b) with full 95mm gap between celotex and sarking felt. Any difference in vent effectiveness between the two options? (It would make the insulation easier to put insulation only under the rafters but I only want to do this if it helps and there is a good chance it will eliminate any issues)
2. Would the 20mm gap each side due to strap noggins likely to cause problems? If so would drilling holes in solve them?
Massive thanks for any insight - I just don't have the experience on this to know what is the best alternative.
However a roofer has told me that I would need scaffolding to install these and this makes the vent upgrade job somewhat expensive (he was saying £800 for scaffolding £250 for parts and (I guess) a couple of days making the total close to £2k. I'm going to get some more quotes but the scaffolding does add a lot.
So, I'm looking for sensible alternatives but I do definitely still want to do the pitch roof insulation if possible (downlighters, wiring, future maintenance, storage etc).
He suggested to only add a load of additional circular vents to underside of the eaves (as they would be easy to add from a ladder) - lets assume 25km2/m and he was suggesting that this would (probably) provide sufficient airflow across to prevent structural issues. He also suggested if I put insulation under rafters (not between) then the gap would be bigger and would allow this airflow more easily.
Also I have 75mm noggins supporting gable straps in between the last 3 rafter each side (12 straps in total). This will reduce the gap to 20mm (rafters 95mm). I could drill a few 25mm holes in the bottom.
My questions if anyone has got this far!
1. Would this eaves-only venting approach likely to cause damp/structural problems (a) with 50mm gap (b) with full 95mm gap between celotex and sarking felt. Any difference in vent effectiveness between the two options? (It would make the insulation easier to put insulation only under the rafters but I only want to do this if it helps and there is a good chance it will eliminate any issues)
2. Would the 20mm gap each side due to strap noggins likely to cause problems? If so would drilling holes in solve them?
Massive thanks for any insight - I just don't have the experience on this to know what is the best alternative.