Under ( roof ) Tiles Spray Insulation

[Onoff]

The SiL rents her Mum's semi detached bungalow out. The roof, clay tiles I think,  is a bit shot as in there's loads of holes in the "felt". 

 

Asked me if I know anyone reputable who does the spray on insulation system that's supposed to rejuvenate old roofs.

 

First thought is it's a 'kin silly idea and that they should redo the roof properly. Before I go back and say this anyone have experience of the system?

 

Cheers

[Tennentslager]

Sounds like rubbish dodgy give me your money

How can it insulate or keep water out?

[Lin]

No direct experience. I have heard of spray on foam insulation that goes underneath the tiles. I think it might have been featured on 'that's life' or some consumer type program. From memory, some people might get problems of rot to the timbers. Also roof ventilation can be compromised and condensation issues in the loft etc.

[Temp]

20 hours ago, Onoff said:

The SiL rents her Mum's semi detached bungalow out. The roof, clay tiles I think,  is a bit shot as in there's loads of holes in the "felt". 

 

Asked me if I know anyone reputable who does the spray on insulation system that's supposed to rejuvenate old roofs.

 

First thought is it's a 'kin silly idea and that they should redo the roof properly. Before I go back and say this anyone have experience of the system?

 

Cheers

 

 

Where is her existing loft insulation ? If it's on the floor of her loft then the space above the insulation is meant to be ventilated to avoid condensation issues. If you now put insulation at the rafter level you would have to ensure that there is no ventilation below the new insulation it or it's just a waste of money.

 

There are two conventional ways to put insulation at rafter level....

 

1) Cold Roof construction: Insulation between the rafters. Leave a 50mm ventilated void between the membrane and insulation. This is to allow any water vapour that gets through the insulation to escape rather than condense on the rafters causing them to rot. As an alternative the insulation can be put in contact with the membrane (eg no ventilated gap) if the membrane is vapour permeable.

 

2) Warm Roof construction: All the insulation above the rafters so the rafters are on the warm side where there is no condensation.

 

Aside: Marketing departments hate the term "Cold roof construction"  because "cold" has negative connotations. Some places now refer to insulation between rafters as creating a "warm roof" but what they are talking about is the temperature of the loft NOT the temperature of the rafters/roof members.

 

Spray foam...

 

I think spray foam is normally sprayed directly onto the underside of whatever felt or membrane is there so it is most like option 1) Cold Roof construction. However if the existing membrane isn't vapour permeable I have to wonder how any water vapour that gets through the insulation escapes? Is there a risk of interstitial condensation occurring on the rafters?  Perhaps they remove any membrane that isn't vapour permeable and spray onto the back of the tiles?

 

If the membrane is in poor condition any water that gets under the tiles can presumably find it's way into contact with the rafters. However currently there might be enough ventilation of the loft that it doesn't matter. If you spray foam all over the rafters so they are no longer ventilated, so is there a risk that this water will become trapped causing rot?

 

Some info here..

 

https://www.which.co.uk/reviews/insulation/article/spray-foam-insulation

 

Quote

An installer should carry out a survey before beginning the job. This usually includes a U-value calculation and

condensation risk calculation. This shows how well-insulated your home is (a lower U-value equals better insulation) and assess the risk of condensation occurring in the structure of your home (interstitial condensation). It should identify any problems and what measures are needed to prevent them.

 

I'd want to know who pays if there is a problem.

 

Edited March 3, 2018 by Temp