A number of 'system' house-types were developed by the British Iron and Steel Federation (BISF). There's lots of these around, and they present a potential conundrum in terms of insulation. A colleague has come across one with insulated render externally, but believes that the cavity is ventilated! If you were starting from scratch with this house-type, what would you do?

Internal insulation with vapour permeable material is obviously stupid but why would ventilation be required if the insulation is external?

I'd have thought the best approach with external insulation would be to remove as much as possible of the internal insulation to make sure the steel was at room temperature. If you want anything over the steel for aesthetic reasons then ventilate behind it to the room. If not, being able to use fridge magnets anywhere would be a small compensation, I suppose.

Ed,

I suppose if it is steel-clad, then even if it is internally lined, a strong magnet will hold. Visions of electro-magnets holding everything to the walls! BIG crash when there's a power cut!

Ed, DarylP: My understanding is that, as it has been 'improved', the cavity (so I suppose the whole depth of the steel frame) is ventilated. So the consensus is (?) that that needs to be blocked. The steel should then be at room temp so corrosion should not be an issue. But should the cavity be ventilated from *inside*? Particularly if everything else were left 'as built', there'd be a thin layer (thickness unknown) of mineral wool between plasterboard and steel. I think this may serve to cool things sufficiently that the steel may be colder than room temp, and thus attract condensation.

What do you think?

Steel is one of the more recyclable materials so the knock it down argument is (even) stronger in this case than most.

Still it's interesting to compare with qeipl's suggestion on a recent thread of progressively filling out a grain silo construction:

http://www.greenbuildingforum.co.uk/forum114/comments.php?DiscussionID=9181&page=1#Comment_148230

though when I previously read it I took him to mean external insulation. I'm far from convinced about his suggested internal insulation - comment made on that thread.

It's not mine! I am 'airing' (ventilating?) this for a colleague. I think the issue is going to be trying to stop the ventilation, as it already has some (unknown how much) EWI. Do you think the cavity should be ventilated to the house, or that there should be an attempt at a VCL at the plasterboard/room 'interface'?

Thanks for your input.

Oh, and yes, I am pretty sure it's a semi....

Nick

Hi all, I live in a British Iron and Steel Federation (BISF) house which I have been insulating myself.

First of all, a Howard House is something different from a BISF house. They are both steel-framed houses, but to different designs. The BISF house is by far the more common of the two with over 30 000 built, while I believe about 1 500 Howard Houses were built. I don't know much about the Howard House apart from that, but the above diagram is of a BISF house. The BISF house had a design life of 65 years and in the 80s when studies were done on defective housing types, it was found that they should last as well as a traditionally built house of the time - they should not be confused with the temporary prefabricated bungalows that were built at around the same time.

In the original construction, the cavity is open to the loft to provide ventilation. There are also ventilation grilles in the upstairs rooms just below ceiling height that open into the cavity. Though in theory the design is vulnerable to condensation and corrosion, I have found little sign of it when I've exposed the steelwork from the inside and from speaking to others who work on them serious problems are rare.

I have found that while it isn't up to modern insulation standards, it is a lot better than many people would imagine, certainly better than a house with solid masonry walls.

My solution to insulation has been to strip out the inner lining of the walls (plasterboard or hardboard(!) on timber studwork) together with the original glassfibre insulation and insert 70mm Kingspan/Celotex into the cavity, leaving an air gap for ventilation behind, before rebuilding the studwork and putting up new board.

You can see some of what I've done at: http://bisfhouse.com/internal-insulation-project-of-bisf-bedroom-by-ed/

Here are some photos. To give a little background, the BISF house is a 3-bedroom double-storey house almost always semi-detached (as here) but occasionally built as a short terrace.

This is the back (2nd) bedroom before work. You can just about see the ventilation grille behind the far lamp.

http://farm9.staticflickr.com/8173/8044266212_f43b9070a5_b.jpg

Here it is with the inner lining of the walls stripped off. The party wall is of traditional construction with two layers of concrete blocks but not load-bearing, to provide a fire-stop and sound barrier. The brown paper encloses glass-fibre insulation nailed to the back of the exterior walls.

http://bisfhouse.com/wp-content/uploads/2012/03/IMGP54331.jpg

http://bisfhouse.com/wp-content/uploads/2012/03/IMGP54351.jpg

With the original insulation stripped out so you can see the back of the profiled steel cladding and steel frame.

http://bisfhouse.com/wp-content/uploads/2012/03/IMGP5438.jpg

http://bisfhouse.com/wp-content/uploads/2012/03/IMGP5439.jpg

New 70mm insulation put into the cavity and new studwork built in front.

http://bisfhouse.com/wp-content/uploads/2012/03/IMGP5444.jpg

http://bisfhouse.com/wp-content/uploads/2012/03/IMGP5443.jpg

50mm insulation in between the studwork

http://bisfhouse.com/wp-content/uploads/2012/03/IMGP5445.jpg

Reboarded, skimmed and painted. The picture rails and fillets originally covered the joins between the boards but are now purely decorative to retain some 1940s feel.

http://bisfhouse.com/wp-content/uploads/2012/05/IMGP5447.jpg

Posted By: RobinB

Posted By: Ed Daviesbeing able to use fridge magnets anywhere would be a small compensation, I suppose.

love it!

Lol, I haven't tried it. I suspect if if did work, it would only work upstairs on the external walls as only they are clad in profiled steel. There's actually a lot less steel in the structure than I imagined due to the lighweight nature of the cladding and roof- the steel uprights are about 1.5m apart horizontally and C-sections of about 60x60mm. Downstairs they support 50mm of concrete render on expanded steel lattice laths as an external covering, a bit like a more modern version of lath and plaster.

Here's a photo of a prototype BISF house under construction from www.bisfhouse.com, those that were finally built differed a little especially in the roof structure (fewer beams at ceiling level and roof trusses of tubular steel) but the wall structure is basically the same.

Copying and pasting the URLs for the images into new tabs allows all to be viewed. If your browser doesn't like some of them then try editing out two of the extra slashes at the beginning, i.e, turn “http:////bisfhouse...” into “http://bisfhouse...”.

Atomicbisf, you can help by editing your post. Use the “edit” link at top right of the post (it'll only appear on your own posts). Get rid of the extra slashes. Also, when you save the changes change the “Format comments as” radio buttons immediately below the main comment box to “Text” rather than “Html”. The forum software should then linkify the URLs.

Why not just spay PU onto the steal like they do with boat hulls?