Insulated roof as part of TV house refurbishment

[Bluestars]

The other day on TV Ch 4, a show called Grand Designs refurbished a house in the East End of London. Part of the job was replacing the roof with an insulated one.

From the shots it appeared the roof was formed thus: New more substantial rafters. Close boarded over with ~20 cm thick planks (not T&G). Waterproof membrane fitted over close boarding. Battens fitted over this for slates (simulation in this case I think) Mineral insulation fitted inside between rafters retained by horisontal battens. Plaster board or similar to finish inside.

I've often heard of a 'close boarded roof', and as the lining paper on my roof is split in many places I might like to re make it in this fashion.

Many have contributed here about insulated roofs, but I don't recall this method being described. They usually mention the use of a special 50 mm insulating material made specially for roofs rather than timber cladding.

Any views on this close boarding method?

Roger

[Hugo Nebula]

On Sat, 20 Sep 2003 22:09:17 +0000 (UTC), a particular chimpanzee named "Bluestars" randomly hit the keyboard and produced:

Timber sarking is AFAIK common (or required) in Scotland. There should have been counterbattens over the sarking board, or maybe they were between the membrane and the sarking. I'm not sure, but one may still have to ventilate between the insulation and the boarding, which would reduce the thickness of insulation which could be used. Mineral fibre is certainly the worst choice in these circumstances, as it is impossible to lay from underneath without bunching it up, and it will also sag over the years blocking up any ventilation path. It also has a low insulation value for its thickness (although it is cheap).

I didn't see the programme, but this doesn't sound like the best solution in terms of 'upgrading' a roof. A better approach would (as you say) to use insulation (Celotex, Polyfoam, etc) over the rafters instead of timber boards. Even if it were only ~20mm, it would give a lot more insulation value than mineral fibre alone. The remainder of the gap between the rafters could then be filled with 75-100mm Celotex or 100-150mm Jablite or Polyfoam to give a reasonable level of insulation.

[Bluestars]

One advantage of the close boarded wooden sarking appeared to be that it could be safely walked on. This seems important because once the roof is covered -with Celotex sheet or wood - the position of the rafters cannot be seen, apart from the nail lines. I doubt if 20 mm foam would be safe to walk on, though a bit of 50 mm I got hold of seemed quite strong.

In the case of the house shown, the intermediate floors had been removed so it was quite a fall if anyone had gone through the roof. The programme was really about the trials and tribulations of the whole house refurbishment, so the details of the roof were rather sketchy, my description was from observation of the views shown.

Roger

[IMM]

There is insulation called Actis that is a sort of bubble wrap that is 25mm thick and equiv to 200mm of rockwool.

[N. Thornton]

Hi. Whats your alternative roof suggestion?

Cavity walls are used in wet windy countries to stop rain that hits the wall soaking through to the inside. That's primarily why we use them.

Regards, NT

[IMM]

A warm roof like most other countries.

Cavity walls were introduced in the 1920s. There was a building boom to prevent unemployment and a skills shortage too. The cavities hid the poor quality of the bricklayers, as water was penetrating through the solid brick walls. It is not mandatory to have them.

[Andrew Gabriel]

Depends where you live. In costal and other windy/wet areas, you will find them in 19th century properties. They gradually migrated outwards from those areas.

[IMM]

In wind driven coastal areas they make sense. In those regions you will also find houses are rendered to seal them in. There is no need to have cavities in a modern housing estate, as wind driven rain, like on the coast, is very rare indeed. Cavities are in coastal areas of Denmark and Holland. The Germans think we are mad to build two expensive walls instead of one, and then have a cold roof wasting space, and further wasting space by not having a cellar.

The best thing people can do with cavities is have them filled with polystyrene balls. Apparently these do not take water from the outer wall to the inner and greatly improve thermal performance. I believe a house with polystyrene balls cavity wall insulation will sell well, or even improve the selling price.

[Ben Harrington]

My house was built in 1866 and has cavity walls.

Ben

[IMM]

It probably has and was. If you were reading the thread you would have gleened that cavity walls were introduced as a defacto standard in the

1920s. They have been around for very long time

[N. Thornton]

Hi

Myth. Victorian cavity walls were usually half inch cavity, though their ratbond walls were IIRC 4" cavity.

solid

I've seen some unbelievably bad bricklaying, and never was there any chance of that happening.

We had some today.

the latter I do agree with. Equally mad not to have the roof just one foot higher and have another useful floor under it.

Cellars are relatively expensive compared to another floor on top. And our history of poor cellars means buyers dont normally want them.

Regards, NT

[The Natural Philosopher]

Indedd, catsles had cavity wall that were filled with any old crud, including teh odd defrocked priest, cats to keep the witches out, and the bodes of enemies etc.

Leaving the cavity more or less empty was a rather more modern develepment tho :-)

[The Natural Philosopher]

Yeah. My sisters last German house with its really well constructed cellar, suffered badly from blocked main drainage flooding all the cellars in the road.

Always a nice homecoming.

Now she has retired toi Fgreece, where the water comes in a big tanker twice a week :)