Re: Cost of loft insulation £7-8k!!!

[m0llyr0se]

We are about to have the major part of our roof replaced and we have to upgrade the insulation to get sign off from building control.

It is a 4 bed 1920s house and, having done lots of reading up on warm and cold roofs and the need to breathe, I got a quote from a reputable company who seem like they understand venting and breatheable materials etc. but it's £7-8k!!! When I look online the cost of roof insulation is around £600 for fibreglass or maybe £1300 for celotex inc. labour and the Superfoil I chose is £20 per m2 but still!

Any ideas or suggestions or recent experience please?

I thought warm and cold roof stuff was about cabin / garden office type buildings?

are you looking to use the roof space for bedrooms , bathroom ?

I think it's where you put the insulation - if you insulate the joists / floor then it's a cold roof and if you put it on the rafters it's a warm roof. We're not planning on using it as a room - just storage - but the floor has already been 100mm insulated and boarded and to take that up and raise the joist height then add insulation and reboard is also expensive and lowers head height.

You shouldn't need to raise the joist height. Just put little feet/risers under your loft boards to raise them up so you can fit more insulation in.

We installed our own (well, dh did most of it) in between the roof joists. It was delivered on a lorry from one of the big diy stores. I can’t remember the cost now, but it wasn’t difficult to do only issue was the time taken.

Thanks Sprig - I'll look into it. It's time and a bad back as well so I was hoping to get someone in to do it for me :)

I'd be surprised if building control would let you have two separate layers of insulation due to condensation risk. Have the designers fine a condensation risk analysis? Lofts are already a nightmare for that anyway especially if there are down lights in the bathroom.
If you want the insulation layer at pitched roof level you'd really need heating up there or at least excellent airflow to make sure it doesn't turn into a damp cold void.

That's really helpful John - thanks. We do have downlighters in the bathroom upstairs ... they've not been out yet to finalise the quote so I guess they would look at condensation risk at that point.
So is installing on the joists and the rafters a bad thing to do from a condesation point of view?

Yes it's a bad thing because the loft will be cold but not ventilated (as any ventilation would negate the insulation), so any humid air coming through from the house will not be able to escape, but the temperature will be cold enough for it to condense out. Over time it will build up potentially and cause damage.
Usually a space would be either heated and insulated, or well ventilated to outside.
Even having an unused loft conversion or bedroom with the heating off up there, you can have trouble with condensation.

I did my own with wood fibre batts between the rafters. Very easy to install but it is a warm roof setup. Surely superfoul is a condensation risk? I would insulate at floor level in your setup.

We have a 3 bed 1930s semi and ours cost £400 (cold roof) as part of our full re-roof. It all got signed off recently for the building regs.

John - Thanks again - it's really obvious when you explain it like that and Vera yes, I can see now it would be a condensation risk as the ventilation would be behind the superfoil!

FManc that's very cheap! My roofing company don't do the insulation so I was expecting it to be more expensive but only by a few hundred!