Is our roofer mad? Raise roof height to fit insulation?

[tony1851]

perhaps a case of gold plating?

Or perhaps not. Perhaps a case of not fully understanding the regs.

 

[Xenon]

Woody is bang on, however, I would push the 15 year payback on it .

 

[^woody^]

I'd rather not add insulation under the rafters as a couple of the rooms have been recently decorated so I need an acceptable amount between rafters.

You dont need to add any beneath rafters. When the tiles and felt come off, the roofer puts the celotex between the rafters. Its such a small area that this is enough to remove the condensation risk and increase the heat retention (celotex = the equivalent of approximately double the insulation in quilt). Just ensure that this joins up with the horizontal quilt on the flat ceiling

You may or may not get some pattern staining where the sloping rafters are (dark lines) but this tends to take about the same time as you would redecorate anyway

 

[dhutch]

I have to admit, if it where me, and I where reroofing my house with the 4inch (100mm) rafters I have, I would put down 50mm of foil sided 'kingspan' between each and slap the roof back on. Not ideal, but lots better than nothing, if you want to add another layer from the inside under the rafters retrospectically theres nothing stopping you doing that. Mine is also a semi det, which all but rules out rasing the roof 50mm without it being very obvious and making an uneven join.


Daniel

 

[tony1851]

Apart from fixing battens on the tops of the joist being unusual practice, there is the issue of what happens at the ridge. The ridgeline would probably have gone up about 2.5", and planning permission is required for anything above existing ridge height.

 

[SurreyRoofingEstimator]

Woody is correct that the works are notifiable and the local BC will advise of any upgrade of insulation required.

We've had similar issues with vaulted ceilings and have been advised to use a product called TLX-Gold which is an insulated breather underlay plus rigid insulation between the rafters over the sloping ceilings

 

[thompster]

Hi everyone, thanks for continued advice.

I spoke to the roofer today. The story is he is a member of something called 'Competent Roofer' (www.competentroofer.co.uk), which is a Government-backed scheme under which suitably qualified roofers can self-certify their work instead of having local building control do it.

The gist of it seems to be that if you are certified you are expected to comply with regs as closely as possible, all work specs are reviewed and spot checks are carried out. That of course is a double-edged sword: on the one hand you get a fully compliant job, on the other hand I could save money with a less thorough firm if local building control are less inclined to poke around and more willing to compromise.

He has said he will submit a spec with less insulation and see if it's approved. If not, he also said that TLX Gold would do the job, the downside being that its apparently quite pricey - though offset by not needing to batten all rafters.

Of the roofers I've spoken too he's by far the most competent sounding and roofs he's done a few years ago still look mint so I'll see what comes back on the revised spec,

Cheers,

 

[^woody^]

You should not be installing any rafter insulation other than at the small area where the pitched ceiling is in the room. Otherwise you are insulating the cold roof space, which is not only a waste of time in what you are trying to acheive, but can lead to condensation and rot issues as warm air gets into the cold loft

I can't see why you would want to use any expensive insulation when there is a cheaper way of doing it - which is also a better way with less to go wrong

 

[thompster]

Hi woody, that's exactly what they have proposed. The additional insulation is in the eaves only to increase the U value where there is only 4 inches between the top of the ceiling pb and the undersides of the tiles. There is no suggestion of using it across the whole roof.