quote Roof replacement and insulation install

[Matt89]

I live in a semi detached Victorian house with a loft room. It’s a pitched hipped roof with 2 dormers. Currently there is absolutely no insulation in the roof and it is very draughty, the room is completely unusable in the winter and there’s no door so getting it insulted is a priority. There isn’t much space between the roof tiles and the plasterboard so the ceiling needs to be dropped to accommodate 75mm PIR boards. Turns out the tiles are asbestos so need replacing as well.

 

I have received a quote for £60k including VAT to get it sorted - this is way higher than I was expecting. It covers scaffolding, skip hire, new roof batten, new tiles, eave protection trays, new breather membrane, new ridge tiles, 75mm PIR plus gapotape, dropping ceiling and replastering, re-rendering the chimney stack and redoing the roof on a bay window.

 

That is quite a bit of work but still seems like a lot - is this in the ballpark of reasonable?

[Iceverge]

I can't comment on the price,how big is it? There is a lot of work involved in this however. 

 

The spec for Insulation and airtightness isn't great . U value of about 0.5 with 75mm PIR between rafters. 

 

Do you know what the spec of the roof is at the moment? How deep are the rafters etc? Any pics? 

 

[Redbeard]

You refer to dropping the ceiling. When you insulate from above during re-roofing, you are allowed effectively to 'get away with' an inadequate level of insulation - because that's all that will fit - with the relevant ventilation gap - between the rafters. If you drop the ceilings you have the opportunity to do the full depth - 150mm at present if using PIR, representing a U value of 0.16W/m2K - so you have to do it, unless any get-out clauses (such as lack of headroom above stairs, for example) apply.

[nod]

It would probably be worth getting more quotes 

 

Whatever insulation you put in You will notice a massive difference 

[Thorfun]

The asbestos removal will be pricey as well I think. You didn’t say it was included in the price. 

[Matt89]

Thanks for your input everyone!

To fill in a few details - the footprint of the house that the roof covers is about 7m x 9.3m.

 

Some details on the current roof:

• Rafters are 50mm deep, the bitumen is laid directly on top of them
• The purlins fixed beneath the rafter are between 100mm and 110mm deep (very old timbers so a mix of depths)
• Plasterboard is fixed directly to the rafters, and buts up to the purlins so you can see the purlins inside the room
• That leaves a 50mm air gap between the top of the plasterboard and the bitumen for ventilation
• The cross beams and hips are about 300mm deep
• There is absolutely no insulation present in any part of the roof, and no eaves trays - when the wind picks up you feel it blow through the room (so I guess it's well ventilated at least!)

In terms of the amount of insulation to put in - given there is nothing at all and it's extremely draughty, putting in anything is going to make a huge difference. Having measured again in feels getting in 100mm PIR should be totally doable by having the plasterboard fixed to the level of the bottom of the purlins. 150mm is going to get a bit more complicated as it would mean re-doing all of the cupboard doors and likely not leaving enough clearance for the radiators. I will need to check in with the regulations - if it's mandated that 150mm has to go in it's going to be a bit more complicated.

 

 

[Matt89]

The plan is to keep the 50mm gap the rafters create between the breather membrane and the insulation 

[Iceverge]

The decor in the room looks just fine ATM. It'd be a shame to loose much more space and have to redo it unnecessarily. 

 

You could strip off the roof from outside. Put 50mm of batt insulation between the rafters. Then add a layer of 18mm OSB. Tape all joints as an airtighess barrier. Important to seal this at the wall plate. Noggins and some sealant should do.  100mm PIR over the top, membrane, battens . 200mm screws through the lot. Counterbattens for new tiles.  

 

 

Should be no need to disturb the inside, no mess inside the hosue. No hauling materials up three flights of stairs.  It'll need to be done in stages/or in good weather however. 

 

U value of about 0.18 which is quite respectable. 

Edited April 27, 2023 by Iceverge

[larry]

 

On 27/04/2023 at 16:35, Iceverge said:

 

 

You could strip off the roof from outside. Put 50mm of batt insulation between the rafters. Then add a layer of 18mm OSB. Tape all joints as an airtighess barrier. Important to seal this at the wall plate. Noggins and some sealant should do.  100mm PIR over the top, membrane, battens . 200mm screws through the lot. Counterbattens for new tiles.  

 

 

Should be no need to disturb the inside, no mess inside the hosue. No hauling materials up three flights of stairs.  It'll need to be done in stages/or in good weather however. 

 

U value of about 0.18 which is quite respectable. 

 

This sounds like a very good plan... 

One advantage of crossing the insulation like this is that it's actually really hard to fit PIR between rafters/joists in any case, at least not without creating a lot of gaps. Of course you can foam them in... Though In our case I paid somebody to put PIR between the timbers outside of our bay window. Was curious why I didn't notice much difference,but this year hacked the plaster off internally and noticed a 0.5-1cm gap all the way round the boards. 

 

£60k is a lot of money, and warrants getting several people to quote who may all suggest somewhat different methods. 

You might as well get some PV up there while you're at it though....!!