I am working on a low-energy retrofit at a modest terraced house in Liverpool. The roof is partly inhabited with a low room under the ridge. Our proposal is to add insulation above the existing rafters, but the planners have refused us planning permission on the basis that this would mean raising the ridge line and "would result in an incongruous, obtrusive and unduly prominent feature within the street scene and would cause considerable harm to existing visual amenity."
We knew that such a response was likely, and we actually submitted an alternative application where the roof is insulated from below. This has been granted approval, but particularly now that we have estimates of the cost of dropping ceilings to give us a bit more headroom, we are keen to question this policy through a Planning Appeal. The client was formerly a councillor- Liverpool's first Green Party councillor in fact - so he is not unused to pushing for changes in policy.

We want to argue that placing insulation outside the rafters is inherently safer from a condensation point of view, as well as allowing more headroom inside. We see this as a fight that may be worth taking on for the whole city (and wider?) rather than just one house. It could be useful to have expert opinion to support us in our Appeal. What evidence would be best to show. (We need to get the appeal statement in before Christmas best by say 18th December)

Dead on. My preferred method by a long way, provided (usually) the roof covering is going to come off anyway (otherwise a big cost penalty). Sounds like you have some other compelling incentive.

The build-up I have settled on is same as for stud walling, in fact seamless with same. After stripping slates, battens, felt, sheathe over the rafters with 11 OSB3 gapfilling (polyurethane expanding) glued and screwed/power-nailed, incl glued to noggings where unsupported. That makes the OSB3 into a moderately vapour-permable, well airtight layer, at least half way outboard in the sandwich, assuming some insulation on top of the rafters, some between the rafters.

On the OSB3, say 150 EPS glued on, then breather felt, then 35x50 downslope battens long-screwed carefully to only penetrate the OSB where it's on top of a rafter, then slating battens and slates. Continuous 25mm-equivalent (e.g. Glidevale FV250) ventilation along both eaves, directly beneath the slates i.e. above the breather felt, ventilating from eave to eave via the 35mm high downslope batten space. The downslope battens strongly connected to their opposite-slope twin, so the whole weight 'hangs' over the ridge, otherwise it will all soon enough begin to slide down the slope.

According to my WUFI studies, in southern England at least, this build-up needs no VCL at all, in fact performs best without, even an 'intelligent' VCL. BldgInsps may want serious proof of that.

I have built this on detached houses, not unfortunately on uniform terrace (or semi detached). Will be glad to help any way you like.

If it's 150 EPS on top of the above described 11thk OSB3 sheathing, plus 35h downslope battens and slating battens 6 thicker than original, the step perp to the roof slope will be 202mm, less slating thickness say 20mm = 182mm. That's enough for a handsome barge board say 119 high with 63mm clear space beneath it.

The other thing to consider at this stage is what the adjoining neighbours think of it all. You'll likely need their consent to alter their roofs so you'll want them on side

Posted By: GreenPaddyNot sure if you have an appeal process like here in Scotland

In England it goes:
1. Planning Officer - decided on Delegated Powers, signed off by the Planning Manager or a Senior Officer; (90-95% of applications dealt with on delegated powers)
2. Planning Committee - if "called in" by an elected district or borough Councillor, or some other trigger set out in the Council's process, e.g. larger schemes or lots of objections. The Planning Officer writes a report for the committee meeting, making a recommendation to approve or refuse, but the Committe can overturn the Officer's recommendation either way. This is the political element of the planning system.
3. If refused, Appeal to the Planning Inspectorate, they are a body independent of any Council that works for the government and are all paid civil servants. If you appeal, you are appealing to the Secretary of State, via the Planning Inspectorate. They assess it based on National Planning Policies but also the policies of that Council that refused it, and all other material considerations e.g. caselaw.

4. If your Appeal is refused, you can take it to the High Court (Judicial Review) but only on the grounds of a procedural issue. Expensive.

4(a) If you are an aggrieved third-party (e.g. neighbour) that doesn't like a permission that has been approved or granted at Appeal, your only recourse is Judicial Review and that has to be done within 6 weeks of the decision. Also only on procedural grounds. Expensive.

@djh I'm new to this forum, and I can't see how to attach a photo. Your suggestion (if I’ve understood it aright) of changing the pitch just below the ridge seems incredibly complicated and visually inelegant, just to comply with the letter of (as I see it ) a poorly conceived rule.

@fostertom My inclination is to strip off the tile and battens and to build up from the rafters, starting with a vapour membrane which would be about half way through the overall insulation. I’m not a great fan of petro-insulants though they have their place, so I would be looking at say 140mm of rigid woodfibre board topped with a breathable felt and counterbattens. There would also be insulation between the rafters – there is some there already to bring us down to a reasonable U-value.

Laying the VCL (and airtight barrier) in this position is geometrically straightforward where it does not need to be wrapped and sealed around purlins, hangers and the like, and of course any . The alternative constructions implicitly promoted by the council policy are either a cold roof with the roofspace not inhabited at all (not really an option in these houses which have always had parts of the topmost bedrooms directly under the roof) or to add insulation below the rafters, which is more complicated to get airtight and leads to greater condensation risks.

@philedge That step is presumably what the planners are concerned at. There are similar-looking steps elsewhere on the street as it drops steadily down the slope. We are approaching the neighbours. There were certainly no outcries from that quarter at the planning stage.


@greenpaddy

@Domnic Cooney It’s not in a conservation area – nor is it listed. Doing many houses together would of course be preferable, but this is one homeowner trying to do their bit. Our hope is that with a relaxation of their arbitrary ridge-line rule, this kind of insulation may be added house by house to end up back with more-or-less consistent ridge lines across the city. The roof finishes in this and surrounding streets, presumably all Welsh slate originally, have been changed piecemeal anyway are now a mix of different colours of clay and concrete tiles with some slates remaining on some houses. They may all be replaced by PV tiles in due course anyway.

We did hope to get the application “called in “ by the local councillor, but he was in an accident at the crucial time, and it didn’t happen. We are going to Appeal, and we need to get this together in the next week or so.

Posted By: Dai Gwynne@djh I'm new to this forum, and I can't see how to attach a photo.

Where you type your post, you should see various things below it. Somewhere in the middle it says Attachments and below that is a button labelled Browse... followed by the text No file selected. Click on the Browse button and choose your photo. The text will then change to show its name. Be warned that the site is restrictive as to the size of attachments - you may need to reduce the resolution of your photo to get the size down (500 kB max IIRC).
You may also not see what I see, depending on what device you are using, and which version of which browser on that device. I have good luck with Firefox on my desktop computer. Others experiences vary

Your suggestion (if I’ve understood it aright) of changing the pitch just below the ridge seems incredibly complicated and visually inelegant, just to comply with the letter of (as I see it ) a poorly conceived rule.

It sounds like you've understood my suggestion. I didn't claim it wasn't complicated, although it doesn't sound too difficult. I certainly never claimed any elegance for the result. I know a lot of people have problems with the ridge height rule, but it does seem to be enforced fairly rigidly. We have a barrel vault instead of a ridged roof in order to stay below the ridge line of the adjacent listed cottage.