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I-Beam vs Standard timber


Nick1c

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We hope to get planning for our new build in the next couple of weeks and I am starting to explore methods of building. The house will in all probability be timber framed & I would like to understand the pros & cons of using I-Beams as opposed to regular timber with regard to ease of building, performance and cost.

I-beams are lighter, which might affect cost [less timber] & transport, but does the cost of manufacture outweigh the reduction in timber used?

An I-beam frame will have a lower timber fraction than a standard one, which presumably makes low u-values easier to hit.

I assume services can easily be routed through the web, removing the need [and cost] of a services void.

Can an I-beam frame be insulated with wood fibre batts or does it need blown insulation?

Regular timber is presumably more easily available & commonly used.

With regards to insulating I hope to be using either wood fibre or blown cellulose. There is the possibility of self-installing wood fibre to save money, we would need a contractor for the cellulose. Given the location of the house [overlooking the Atlantic at the end of Cornwall] I am paranoid about penetrating damp. If cellulose gets damp does it loose it's thermal qualities?

 

Nick

 

 

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I am considering using the I-beams for shell rather than the first floor. I have seen that type of joist on builds round here and wondered if there is much spring in the floor once one is laid, I presume they are stiffer than they look!

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I can't answer your specific questions about using I-beams for walls, but I did look in detail into using them for joists, vs solid timber.

For my 16ft span, solid timber would have worked out about £20 per joist, whereas my JJI engineered I-beams of the same dimensions were £36 each. So you are paying nearly double, for a considerably reduced quantity of timber! But the benefits are enormous.

- much easier to handle due to reduced weight

- totally dimensionally stable, giving perfect flat and squeak-free floors

- easy running of services through the web

- far better thermal properties because thermal bridging is almost eliminated

 

To me, it was a no brainer to go with the I-joists. In the grand scheme of my build, it added less than £300.

 

For walls, I believe that a Larsen truss may be a more common way of achieving what you are looking at.

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7 minutes ago, Crofter said:

For walls, I believe that a Larsen truss may be a more common way of achieving what you are looking at.

 

Particularly if you're going to fill the walls with cellulose, as the Larson Truss effectively eliminates cold bridging.

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@Nick1c it depends on whether you want to hit or exceed building regs. if you wish to acheive min insulation timber is the easiest to source, find a joiner to buid a kit and insulate. if you wish to exceed regs, as many of us do, I beams are one of the ways. choose 350mm to get .1u value with blown cellulose, so no air spaces. you will still have an external cavity so damp shouldn't be a problem. this is the way i'm going though i'm having a service void to alow me to insulate then run water/elec at my leisure.

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  • 5 years later...

Is this still the school of thought ? What did you go with ? Have things changed since 2018? ( yes yes before I get loads of replies like how many prime ministers we’ve had, we now have a King etc I know lots has changed but regards this topic please 😉

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20mm and cement render. 

100mm dense blocks. 

250mm EPS blown beads. 

215mm dense blocks. 

15mm sand and cement and skim. 

 

Should have opted for the 300mm cavity to make it 650mm...

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1 hour ago, Alan Ambrose said:

does that mean you're heading for a 50cm wall thickness by the time you've added rainscreen and service void etc?

 

You only need to put a Service void where you are running plumbing, and in those cases there's often another option, ie within cabinets, or false walls hiding a concealed system, or within bath enclosures, or...etc. etc.

Suitably rated electrics can run within the insulated wall/roof. So you could be at 465mm for a very high performing wall/roof structure. You could go 50mm less on the I-Joist / insulation and still meet PassivHaus targets.

 

image.thumb.png.10d403c076d3dbf81e3556fa2cb8e8b5.png

 

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