Attic Roof Insulation

Can anyone help? We are wanting to insulate between the rafters of our
attic roof which are about 90mm in depth. It is an old house (1900),
the roof is tiled and doesn't have roof felt or sacking so the
insulation would back on to the roof tiles. We have read you need a
space of 50mm between the insulation and the roof tiles and some
suggestions that instead of insulating between the rafters you should
insulate across them. My thoughts are to get some 50mm Kingspan
insulation and leave a 40mm to the tiles given the age of the house
and the fact that there is unlikely to be condensation problems given
the age of the house and there being no roof felt barrier. Is 50mm
enough? Are there any guidelines?
Any advice welcomed - thanks in advance.
Reply to
fixsheff
Having looked at Kingspan TP10 literature it seems to suggest that it is rafter level insulation with no condensation risk - does this mean no need for a gap and the ability to put in a thicker depth of insulation or is 50mm enough? Is TP10 the best stuff for between rafters insulation? Thanks.
Reply to
fixsheff
Best do both - put 50mm kingspan between the rafters, and then overlay the whole lot with big sheets of more of it... in my case I overlayed with plasterboard backed with 40mm expanded polystyrene IIRC.
David
Reply to
Lobster
I tyhink insulating across is a VERY good idea if you have the space. You reduce the problems of cold bridging, and create a really decent airtight vapour barrier as well. You would have to slea teh celotex to the celing below top prevent draights under the celotex of course.
50mm sounds good to me. More is better.
Curious as to why you want a warm loft tho..normal practice would be to insulate the ceiling below..
Reply to
The Natural Philosopher
I think what the condensation bit means is that it is foil covered, and impermeable. It doesn't mean that you don't need a gap.
You need to ventilate those rafters for sure. The air above will be wet in humid weather, and at night you may well get condensation running down the top surface as the temp goes below dew point. That has to be allowed to run away down to the eaves and the residue evaporate.
Polyisocyanurate is the best commercial material for insulation there is. Kingspan and celotex ate the current dogs bollocks.
Thinking more about this, if you have the space, Id be tempted to try and mount the stoff OFF the rafters altogether - to make a 'tent' of insulation underneath, because I am concerned that condensation above the insulation layer may in time affect the rafters: when you take a roof that expects heat to bleed from below to help keep it dry, and then seal that heat off..things change. And you have no sarking..so its slightly unusual.
I would wait for others to add their 2c here.
Reply to
The Natural Philosopher
In article , The Natural Philosopher writes
Although it does take up more space I agree with your last suggestion, if the rafters do get wet for any reason and there is material between them you will have damp timber in an enclosed trench which will have no opportunity to dry out, potentially leading to rot problems.
Reply to
fred
In article , snipped-for-privacy@gmail.com writes:
Why are you wanting to do this? If you just want to insulate the storage space, then 25mm sheet screwed to the rafters would be fine, and you will get nearly all the same benefits as a thicker layer as the benefits don't scale anything like with the thickness. OTOH, if you are looking to insulate as part of a loft conversion, then you'll need to conform to building regs requirments. Also, what if any loft insulation if there already?
Reply to
Andrew Gabriel
In article , The Natural Philosopher writes:
I did this with a lean-to construction roof (over my bathroom). I fixed the underside of the rafters with pressure treated roofing battens at right angles, and then fixed the Kingspan to those (or in most cases through those into the rafters. I provided a vent in the gable end above the Kingspan, and the roofing felt looped down enough to provide further ventilation. The rafters showed some signs of rot which had been repaired (before my time, probably when slates were replaced), and I wanted to make sure they stayed very well ventilated. My worry was not condensation, but any water ingress through the roof which I would likely not notice one the Kingspan was in place, and without ventilation might lead to serious rotting of the rafters.
Reply to
Andrew Gabriel
Dear all, thanks for your replies. I am the posters other half. The loft is actually an attic room that had a low ceiling with no insulation behind it and a couple of plaster board dividers behind which the tiles have always been exposed (not weight bearing walls or anyhting just boards) we want to use the room as a bedroom and insulate it properly, as it was too cold in winter and too hot in summer. It has an original window in the side gable. So we have taken the ceiling down (100 years of muck) so now we have a roof that needs some insulation before we can plaster and redecorate so it is not quite a conversion just a bit of updating. With that in mind. would you give the same advice?, thanks for your help!
Reply to
lorientgirl
Have you investigated Renotherm?
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'd be interested to hear if anyone has used this company or similar. Michael (with a similar problem) .
Reply to
Michael Shergold
Basically yes. All becomes clear. If you have the space, insulate under, if not insulate between and in all cases make airtight and tape it all up. Leave at least some gap above.
Be careful at the eaves..You MAY get water dripping off the top edge of the celotex here. put some kind of plastic sheet to let it come out at the eaves, not down into the walls.
My instinct would be to tape plastic to the underside of the insulation and let it hang over the edges of the rafter bearer plates, before re boarding the thing.
Reply to
The Natural Philosopher
I wouldn't touch it with a barge pole. How does any damp that gets onto the timbers get out again in a timely manner? To me it's asking for the roof timbers to rot. And when the time comes to replace the roof properly it's going to be a right mess and probably require far more replacement timber than otherwise would be required. As a buyer of a property I'd be very wary of place with it, what is it hiding?
In the long term and for sale-abilty you are far better off stripping the roof, replacing timbers as required, putting on a modern breathable sarking and replacing the orginal tiles/slates. You will need some new but put them round the back or something.
Reply to
Dave Liquorice
50mm rockwool slabs between the rafters makes a huge difference, and Celotex even more so. Either would leave you with the recommended gap, but the rockwool packs you can sling in the back of a car rather than having to arrange delivery, and they're a fair bit cheaper. I found the key to a tight fit was to slightly overcut the width, then wedge one end in and run a hand saw flat against the side of the joist, cutting the insulation at the same time. That way any variation in width is accommodated.
Reply to
Stuart Noble
In article , Andy Champ says...
Interesting that roof insulation experts always talk about leaving an air gap between slates and insulation. That product is sprayed directly onto the tiles. Is that the problem with it?
Reply to
David in Normandy
OK, I'll bite. This stuff has been around now long enough to show any bad effects - have any been seen in the flesh?
My (rented) place has the attic done like this. Seems OK so far, but then again I don't know how long it's been in place...
I presume the issue is condensation/rot in the timbers?
Reply to
PCPaul
I might be paranoid, and wrong, but I don't need to take the chance.
When this is on the inside of the tiles the condition of the timbers cannot be assessed. It's been used because there is some kind of problem with the roof, and it hides whatever the problem is. That's enough to put me off.
Andy
Reply to
Andy Champ

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