Insulating roof space

Grandad2b

We have an early 70s brick built house with concrete tiled roof. There is black roofing felt beneath the tiles. There is about 100mm fibreglass insulation between the ceiling joists but most of the area has been boarded out.
We're wondering what is the best way to increase the insulation - do we aim to put some kind of material between and/or below the rafters or should we be taking up the boards, increasing the depth of the joists and installing further insulation before replacing the boards?

paul991

try something like loftzone then replace the boards

Reed_Richards

Typically, a house like yours was built with the intention that the loft space should be ventilated.  Loft floor insulation (like fibreglass) allows air from below to percolate through very slowly and so remove moisture from the house below, enter the loft and then get vented away.  So insulating between the rafters might prevent this or alternatively it might be ineffective if your loft space ventilation is under the eaves.  

mmmmikey

Yes, agree with the above. Had the same problem and took advice, which was to remove the boards, top up the insulation making sure not to obstruct the roof space ventilation and then make a new storage platform on stilts over the new insulation. A messy time consuming job but the effect on heating bills was dramatic and certainly worth the effort.

andyg9053

Do you need it all boarded? Consider lifting all of the boards. Create a walkway on the stilts, you could probably have at least 200 of insulation under that. The remaining area at 300, put shelves up on the roof struts for your storage

Grandad2b

@paul991 Not heard of that before
@Reed_Richards @mmmmikey I think the ventilation is at the eaves. 
@andyg9053 Worth looking at

Reed_Richards

Grandad2b said:

@Reed_Richards @mmmmikey I think the ventilation is at the eaves. 

In which case insulating between the rafters won't work.  Or it won't work unless you block the eaves ventilation and that would be asking for trouble and probably invalidating any buildings insurance cover if trouble arose. 

silverwhistle

I had a similar situation, and when I wanted to upgrade I laid celotex over the boarded areas and then boarded on top of that again.

I've also put reflective insulating foil over the rafters which still allows ventilation at the eaves.

Qyburn

Reed_Richards said:

Grandad2b said:

@Reed_Richards @mmmmikey I think the ventilation is at the eaves. 

In which case insulating between the rafters won't work.  Or it won't work unless you block the eaves ventilation . 

Surely the purpose of the insulation is to reduce heat conducted through the ceilings. And the eaves or soffit vents are to ventilated the space above the insulation. Like the picture on the left here..

Edit .. doesn't want to embed the image, see link ..

https://i.pinimg.com/originals/ba/b2/eb/bab2ebd88bff261b9b92cf1f25a5136a.jpg

mmmmikey

silverwhistle said:

I had a similar situation, and when I wanted to upgrade I laid celotex over the boarded areas and then boarded on top of that again.

I've also put reflective insulating foil over the rafters which still allows ventilation at the eaves.

I was advised against the Celotex approach because it can lead to condensation issues between the different layers and problems with damp in the longer term. Not sure how serious that is in practice but certainly there's lots of advice about not laying insulation on top of the boards 

paul991

moist air from the upstairs rooms needs to be able to escape either though the plasterboard and insulation or a trickle fan in a upstairs room