JJ I joists for external walls

[jamieled]

I'm currently considering the use of JJ I joists for our external walls, partly to allow me to get the insulation thickness we will need.  The web documents suggest that they can supply in standard 2.4 or 3m lengths with other lengths 'on request'.

 

For a couple of reasons we have, at present, downstairs ceiling heights slightly higher than 2.4m.  Has anyone used JJ ijoists for stud walls and did you procure them in non-standard lengths?  How easy is it and was there a significant cost premium?

 

Clearly one option would be to cut the 3.0m lengths to size, but that seems wasteful.  I've asked the same question of JJ with no reply as yet.

[caliwag]

There was a serialisation some years ago, when the Independent was published on paper and had a good property section, about a guy who built a house on a tricky site (a mature tree) using I beam walls with blown paper insulation. The timber work was supplied by this Scottish outfit https://www.jamesjones.co.uk/jji-joists/ who may be able to assist. I believe there was a book published illustrating the process and issues. Most interesting. 

[Gone West]

We have a portal timber I-beam framed house built using Steico I-beams. They came in much longer lengths IIRC 7m, 9m and 13m and were cut to minimise wastage.

[mvincentd]

https://www.homebuilding.co.uk/insulating-the-outside-walls/

 

[Ed Davies]

I'm using JJI I beams for the studs in the gable ends of my A-frame house for the same reason as you: depth of insulation. The house designer, structural engineer, building control and JJI distributor technical/sales chap all happy with that.

 

The one gotcha though is the choice of depth of the beams. I picked 235 mm off their list of available depths just because that was what I needed for my intended U-value. The distributor did warn me that that was uncommon (245 mm being the nearest standard one) so there'd be a bit more lead time. I didn't want to change at that point - the structural engineer had signed off and was being a bit uncommunicative then (been much better later) - so decided I could put up with ordering a few weeks early. I got most of the beams needed for the roof (two packs of 33) fine.

 

However, when I came to order the last few I needed for the roof and the ones for the ends there was a problem: I wanted fewer than 20 (can't remember the exact number) but JJI only supply in packs of 33. For the common sizes the distributor would have been happy to split a pack as they'd sell the rest to somebody else quickly enough but for 235s they didn't want them hanging around. In the end they found a pile of 235s of various lengths and widths in their Glasgow depot which they supplied. They were a bit tatty and needed sanding but were OK for my purposes.

 

Moral of this tale: pick the depth required carefully.

 

As to length, they seem very flexible. I asked for 8 metre lengths and they didn't blink. The extras came in various lengths, the longest being 10m IIRC. If you want just over 2.4m then maybe it'd be best to ask for 5m lengths and cut them in two.

[Jeremy Harris]

Welcome Ed,

 

Really glad you've joined us, especially as I keep referring people here to your great blog entries on the comparison between PV and ST!

[Gone West]

4 hours ago, Ed Davies said:

 

Moral of this tale: pick the depth required carefully.

 

Welcome to the forum Ed. It was similar for us as we needed 350mm Steico timber I-beams but found it was cheaper to have 300mm with a 47x47mm batten nailed to the flange. The 300mm beams were available off the shelf as well. It also made it easy to fit a 47mm ledger plate for hanging the metal web joists.

[Patrick]

How about Price comparison to traditional Timber Framed Walls.

In theorey I-Joist should be cheaper -in reality I always see them for sale at a  higher price then let s say two 2x4s  . I was thinking about doing the same thickness of Wall just double up the 2x4s and leave a 10cm gap in between the 2 . Basically Gives you a very thick wall , Similar to a 300mm I-joist for possibly lower price (this is what im currently trying to find out)