Attic Insulation

[bignose]

I intend flooring my attic and want to insulate with 170mm fiberglass under the roof tiles. When this is done i will use plasterboard finish.
My question is have any of the forum found a way of keeping the 2 inches required for ventilation between tiles and insulation.

[lightfoot]

This could be a trick question or maybe I've missed something?.........but at the risk of sounding obvious the maximum insulation you can install between the rafters is equal to the depth of the rafters less the 50mm (2 inch) needed for cross ventilation.

However you could increase this available depth by fixing 2 x 2's etc to the underside of the rafters or even better you could fix a layer of Kingspan TP10 foil faced PU insulation  http://www.insulation.kingspan.com/uk/tp10.htm  to the underside of the rafters in addition to fiberglass/rockwool between and if you tape the joints of the TP10 you won't need a additional vapor check between the plasterboard and insulation.


Hope that's some help


PS.  I would tend to use a wicked batt (semi ridged) insulation like rockwool flexi  http://www.rockwool.co.uk/graphics/RW-GB-implementation/datasheets/Flexi.pdf  between the rafters as opposed to rolls of insulation, as it is easier to install, more likely to stay where you put it and not sag over time.

[stephen]

you could try these guys for rigid insulation
http://www.secondsandco.co.uk/
I used to work for Kingspan and seconds and co took loads of different boards from us.

Or you could also use plastic netting and staple it into place to hold all the fluffy insulation in.
Stephen

[renewablejohn]

netting on a roll used in agriculture round balers is ideal. just use a staple gun.

We used insulation from B&Q 2 for 1 offer in plastic liner held up with netting then attached the Silver foil insulation (sold as a pack to insulate a garage door hence very cheap) on the inside of that . Ceiling was already filled in with rockwool and fully boarded across

[PerryOne]

Fiberglass is no where near as good an insulation as polystyrene.
It was designed to let water vapour through, where vapour goes so does air.
Far better to fit one of the rigid polystyrene or similar sheets, however, if your roof is in good condition then one of the spray on foams will give you the best result.
Foam will find its way into every space however odd and give you that airtight watertight covering.
Fiberglass is impossible to fit into a roof without leaving some holes, ditto polystyrene and its the holes that waste the heat you've paid for.
Note: In the USA and Canada spray on foams have Government recommendation and are the flavour of the month.

[solar living]

Just a word of caution on spray foam.

I started in the building trade as a roofer and have come across spray foam on a few occasions.
I dont doubt that it works, it sticks like s***.....and that is the trouble!

If you ever need to replace broken tiles then it is a nightmare for the poor roofer. To replace one tile , it would normally take longer to get the ladders out than take out the broken tile and replace it.

One customer of mine had been told that it dosent matter if a tile is cracked or broken as the foam will keep the water out.
True...it kept it out of the roof. The foam is srpayed from under the tiles and it covers all of the timbers as well.
When i managed to get the broken tiles out the timbers under the tiles were wet, which was not visable from inside the roof. If these tiles had not been replaced the roof battens and rafters would have started to rot, with no visable signs from inside the roof.

Also dont forget you still need to ventilate your roof space!
Another customer had this foam installed and had bad condensation problems. The foam had been sprayed down into the eaves, sealing the roof space. We could not easily install tile vents, again because of the foam. So we had to cut away the foam in the eaves.

Like i say, i dont dispute that it works well as an insulation material and has its uses. But if you are thinking of using this product please make sure....
A) Your roof tiles are all in perfect condition with no cracks etc.
B) Dont forget ventilation
 

[Skywalker]

Hello

Go here:

http://www.greenbuildingforum.co.uk/newforum/

and search on 'Skeilings'.

I would use kingsan/cellotex between & under the rafters (lightfoot is absolutely right about using the space between your rafters less 50mm). You can also get kingspan/cellotex etc laminated onto the back of plasterboard which helps to deal with cold briging by your joists. You will need to make sure that whole thing is nicely airtight as well to get the benefit of your insulation and make sure you have enough ventilation at ridge level if you are following the joists all the way up (just to back up solar livings point).

You also probably need planning permission

S.

PS personally wouldn't touch spray foam with a barge pole.

[sealo0]

Hi All

I recently insulated these spaces. I have a Chalet Bungalow and the void in behind the Bedroom wall & Skeilings were uninsulated. This means that large parts of the lower floor ceilings are open the all the draughts.

I cut a hole in the walls on each side of two bedrooms and crawled into the voids. 

The Skeilings joist seen in both pics are 100mm deep. So I got some 50mm Celotex & pushed it up inside the Skeilings. All good fun as all the gaps between (widths) were all different. Thus leaving a 50mm (ish) gap. These were then wedged in place. I was up in the attic last week when it was quite windy & there is still a good draught up there so there is good ventilation, as there should be.

I also added 150mm insulation over the ceiling and hung 150mm on the walls via a latticework of wire nailed to the wood frames.

For the Celotex I went to my local builder merchant (Travis Perkins) & got a price of £25.89+ vat. Looking on Google I got a price of £16.35+vat a sheet (1200*2400) went back to Travis & got the price down to £16.89+vat  (inc dely) which was good as the other price was 200 miles away & they would not deliver!!! But I did not tell them that!!

The improvement is fantastic, last year we have the heating on most of last winter but it has hardly been on so far this winter.

    http://i240.photobucket.com/albums/ff256/sealo0/Houseroom.jpg

http://i240.photobucket.com/albums/ff256/sealo0/house010.jpg

http://i240.photobucket.com/albums/ff256/sealo0/house025.jpg

Hope this helps

Mike   

[bignose]

A simple Question produces such a varied response i knew i was in good company. Being a person that looks into all skips i dont like to wast any material. The insulation above my sealing in itend using, no matter how difficult will end up in the rafters. Im Talking about 50 sq. yards of fluffy stuff.
I have already mooved this fluffy stuff there 10 years ago and have inspected the rafters and (maby lucky) they look o/k. I might add that i stapled a plastic sheet to the rafters holding 100mm of fiberglass in place.
I have a feeling common sense has to play its part and not look for a easy fix .Love you all. BIGNOSE