Warm Roof Construction

ferryman35

There are lots of threads on here that refer to draughty and cold dormers....

For this type of house build is a warm roof build a better option? By warm roof, I mean one where the insulation is placed over and between the rafters.

From what I've found out so far,the benefits seem to be improved air tightness of the building, better noise resistance, better protection for attic run pipes (& tanks), better for the rafters because they are no longer exposed directly to external temperatures, and this design maximises the internal space.

The downsides seems to be the extra cost (labour & materials) of counter-battening and the fact that the fascia board will be much deeper - so who knows what that will look like!

Despite the benefits attributed to it, its a hard sell! Anyone care to offer their opinion?

RITwing

if you cut the rafter overhang so as to lift the soffit higher then the eaves board does not have to be deep.



As for all the other "concerns" - you get what you pay for.
Let the old school dicatate and you will have a cold house.

MicktheMan

ferryman35 wrote: »

Anyone care to offer their opinion?

Do it. You wont regret it. The heating cost savings will pay the extra investment in no time.
Btw, have you quantified the extra cost of a warm roof (including discounting the labour and material needed to get a cold roof dormer to the same airtightness and insulation level as the warm roof)?

ferryman35

Lads , thanks for the replies and I appreciate the detail!

I'm sold on the idea, the problem was bringing everyone else along with me...

We're trying to work out the costs at the moment, but that was proving difficult because so many either didn't understand or want to understand the concept.

In terms of the overall build the main extra expenses are the materials and labour to counterbatten the roof, and the fact that the roofer is more involved in the insulation process.

That aside the construction cost doesn't seem to be hugely different, but where it does get complicated is with the materials you choose.

If I went for a PIR board, the warm roof insulation is actually cheaper than the cold roof materials, and in fact the difference in materials looks like it would go along way towards to extra labour costs.

The major 'BUT' is that PIR isn't breathable, & I don't believe it would be wise to sandwich the rafters between a vapour barrier on the underside and foilbacked PIR on top, because the rafters wouldn't be able to breathe. Does this make sense?

Breathable materials are more expensive and more of them are needed, so the material costs are back up to the cold roof costs + some, to comply with the building regs.

Weighing up the additional costs for the expected benefits it still looks worthwhile. I'm reassured by your feedback and puzzled by the professionals who think its just pie in the sky!

MicktheMan

ferryman35 wrote: »

The major 'BUT' is that PIR isn't breathable, & I don't believe it would be wise to sandwich the rafters between a vapour barrier on the underside and foilbacked PIR on top, because the rafters wouldn't be able to breathe. Does this make sense?

Yes, spot on