Spray applied polyurethane insulation

[vards01]

Hi dont know if anyone has any experience of Spray applied polyurethane insulation in the loft space between the rafters?

I own a 1890 build semi, with the original clay tile roof the problem I have is that when roof tiles where put down they were 'scribed' on with motar, which is proving to be a problem 120 years down the road! The motar has dried out and become very brittle causing hefty draughts crap all over anything thats stored up there and the odd loose tile. Obviously there is no sarking felt installed so the insulation levels are just hurendously poor.

I have come across the Spray applied polyurethane insulation which appears to be a good idea, I have no idea of costs but i'm assuming its pretty cheap, I have a few reservations of this product and would like to know if anyone can offer any guidance.

1) When applied is this stuff really difficult to get off rafters at a later date etc...

2) When expanding does it lift the tiles...

3) Is there any other undesirable attributes?

4) Cause a void for damp/wet rot on timbers?

5) Restrict the roof space ventillation to undesirable levels?

Any advice much appreciated, perhaps there are some alternatives?


Thanks in advance,

Ian

 

[noseall]

Spray foam - NOOOOOOOOOOOOOOOOOOOOO!

 

[big-all]

disadvantages
1 foam is waterproof and dosnt breath so any leaks in the roof means the timber cannot dry out so will rot very quickly

2 roofers do not like foam as it sticks everything together adding time to a re-roofing costing you hundreds off pounds extra

3 tiles will get broken during removal adding to the replacement costs when reusing the tiles

 

[vards01]

I did have another idea which is more labour intensive, but could be easily removed and replaced in years to come when i get a new roof. The below sketch shows my thoughts:

Untitled

• vards01
• 7 May 2009
• 1

 

[vards01]

What would be a good felt to use? I am correct in assuming the scribed motar was intended to keep driving wind, rain and snow out, and not give strength? I can see a problem with my method as any driven rain / condensation would run down and end up on the ceilings of the below rooms?

 

[freddiemercurystwin]

Is your loft for 'comfortable' storage or are you doing a conversion?

 

[vards01]

currently storage......but its a nice size so I would like to do things properly for future conversion.

 

[freddiemercurystwin]

I believe for a conversion they would insist on felt (though I'm not completely sure tbh), whether they'd accept your hybrid system I don't know. Whilst it partly solves your problem and is commendable it also creates another in that if it does leak you will have no way of knowing, it may well be the rafters soak up the water and the first you'll know of it is ending up with a damp patch coming through the plasterboard. It depends on the condition of the tiles and how much of a gambler you are. Secondly the gap between the insul and the tiles will (practically) be just as cold whether the felt is there or not. If you install the felt it needs to be vented at the eaves and at the ridge not closed off so you'd need to make sure this was possible first too. You'll end up with a 'warm roof'. There's one on this page at the bottom: http://www.superglass.co.uk/Roofs.aspx

If you're serious about doing a proper conversion and going through building control you (unless someone else replies with a definitive answer) I'd phone your local Building Control they're quite human and will tell you one way or another.
ps To comply you will need around 130mm Kingspan or similar insulation, 80mm between the rafters and 50mm below, then your plasterboard beneath that.

 

[vards01]

Does this scribing method actually require getting under the tiles? As I am thinking i could redo the motar with a mastic type gun obviously taking out the crumbly rubbish before I appy the new stuff. Then batten the felt on then the insulation then the plasterboard? I just dont really know what to do for the best.....I just know I can not afford to re-roof at the moment. Any advice much appreciated.

 

[vards01]

But its a pretty unanimous opinion that spay foam is a big no no?

 

[freddiemercurystwin]

But its a pretty unanimous opinion that spay foam is a big no no?

Whatever you do do not go the spray applied route. To fit the felt you can just leave a gap at the ridge and make sure air can get in/out at the eaves. As mentioned it depends if you'll eventually be going through building control or not whether you do this now or refelt the roof in a few years, ring 'em up see what they say They might not give a damn about having felt above the rafters too in which case fill yer boots!

 

[vards01]

Spoke with BC didn't really go much on the felt idea or the spray foam, he said best idea would be insulation board with a gap, I could re motar the tiles with a weak lime motar if i wanted but would have to accept that prob in 10 - 15 years I would have to re-roof anyway.

So will prob re motar backs of tiles, and put as much celotex insulation as i can get in obviously allowing for the required gap. Then prob plaster board or hard board over the rafters when im done.

 

[freddiemercurystwin]

Now you know!