New build - confused between timber & i-stud

[osmononame]

Hi all,

 

I am in the process of getting quotes for my self build timber kit. I have managed to get a lot of good advice on this forum so far!

 

One thing I am not sure of is the advantages of an i-stud as opposed to regular timber? I can see the advantages of webbed i-joists as it will make the running or services/mvhr so much easier (amongst other benefits) but whats better with i-studs?

[Crofter]

Better thermal performance, because of reduced thermal bridging. It's also likely to be lighter, for ease of handling, and more dimensionally stable.

[MikeSharp01]

1 minute ago, Crofter said:

Better thermal performance, because of reduced thermal bridging. It's also likely to be lighter, for ease of handling, and more dimensionally stable.

+1

[Russell griffiths]

I’m not sure if you are getting your terminology mixed up. 

An I STUD would be used vertically for building walls

an I JOIST would be used for a floor or roof

a METAL WEB JOIST will be used for floors. 

If you are using them as studs for the walls you can use a deeper stud 225-300mm this way you can fit in more insulation, you will not find many solid timber studs over 145mm so these require a way to get more insulation in so you normally end up fitting insulation over the studs to stop cold bridges. 

[nod]

I stud and timber doesn’t compare 

stronger Straighter Doesn’t warp

Can be independently built upto six Mtrs 

[Jeremy Harris]

17 minutes ago, osmononame said:

Hi all,

 

I am in the process of getting quotes for my self build timber kit. I have managed to get a lot of good advice on this forum so far!

 

One thing I am not sure of is the advantages of an i-stud as opposed to regular timber? I can see the advantages of webbed i-joists as it will make the running or services/mvhr so much easier (amongst other benefits) but whats better with i-studs?

 

Welcome.

 

Probably best to clear up some of the terminology, I think.  i stud is an internal wall metal framing system.

 

The main timber frame external wall choices are traditional solid timber frame, I beams, or twin stud.  I beams were originally designed to be used as joists and rafters, as they are very stiff in bending, but have been adapted to be used for walls, as they thin web of OSB between the two structural members significantly reduces thermal bridging.  Twin stud is pretty similar, two standard studs spaced apart by noggins that, like the web in a I beam, reduce thermal bridging.

 

None of these methods of external wall construction have any impact on running services, as the space between the timbers ends up being filled with insulation.  Space for services will usually be provided by adding a service void inside the frame, made from battening the inside of the external walls.

 

When it comes to floor joists, the choice is really between solid timber, I beams or posijoists.  Solid timber and I beams need to have holes cut into them for plumbing, wiring, etc to run through, posijoists have a steel web frame holding the top and bottom timber parts apart, so everything can be threaded through the spaces in that.

 

[osmononame]

Hi guys, 

 

Thanks for all the replies - I understand the differences of i-stud for walls / i-joist for the flooring (I actually have i-joists in my current house as we could get longer runs with it in the larger rooms)!

 

My architect has specified 145x45 studs with 600 crs with 140mm of Pir/Kingspan with 32.5mm insulated plasterboard on top. With this depth of wall would I see much advantage going with i-studs? What kind of extra cost are we looking it?

 

As far as the PIR is concerned I am looking at blown cellulose as an alternative but can't find anyone up here to quote on it.

[ProDave]

5 minutes ago, osmononame said:

Hi guys, 

 

Thanks for all the replies - I understand the differences of i-stud for walls / i-joist for the flooring (I actually have i-joists in my current house as we could get longer runs with it in the larger rooms)!

 

My architect has specified 145x45 studs with 600 crs with 140mm of Pir/Kingspan with 32.5mm insulated plasterboard on top. With this depth of wall would I see much advantage going with i-studs? What kind of extra cost are we looking it?

 

As far as the PIR is concerned I am looking at blown cellulose as an alternative but can't find anyone up here to quote on it.

If you went up to say 300mm I beam studs you could fit more of a cheaper / easier to fit insulation like Frametherm 35 and have a better decrement delay.

 

No mention in your description of an air tightness / vapour barrier or a service void for cables?  That sort of detail will improve the build probably more than increasing the insulation.

[Jeremy Harris]

32 minutes ago, osmononame said:

Hi guys, 

 

Thanks for all the replies - I understand the differences of i-stud for walls / i-joist for the flooring (I actually have i-joists in my current house as we could get longer runs with it in the larger rooms)!

 

My architect has specified 145x45 studs with 600 crs with 140mm of Pir/Kingspan with 32.5mm insulated plasterboard on top. With this depth of wall would I see much advantage going with i-studs? What kind of extra cost are we looking it?

 

As far as the PIR is concerned I am looking at blown cellulose as an alternative but can't find anyone up here to quote on it.

 

Just to be clear,  I stud is a metal framing system for internal walls, whereas I beams are timber.

[osmononame]

16 minutes ago, Jeremy Harris said:

 

Just to be clear,  I stud is a metal framing system for internal walls, whereas I beams are timber.

Ahh ok - so I didn't understand - but do now - thanks!

[osmononame]

41 minutes ago, ProDave said:

If you went up to say 300mm I beam studs you could fit more of a cheaper / easier to fit insulation like Frametherm 35 and have a better decrement delay.

 

No mention in your description of an air tightness / vapour barrier or a service void for cables?  That sort of detail will improve the build probably more than increasing the insulation.

I dont have the spec to hand but yes there is mention of vapour barrier / everything being taped down. The trouble with going for 300mm i beam studs is that the foundations are already in - presumably we would lose space internally to account for thicker frame? And then there is the cost which I presume will be more?

[Russell griffiths]

As far as I’m aware your smallest I joist would be 195mm so a bit bigger than your solid timber, and these will be a pain to fit pir into 

 

[ProDave]

45 minutes ago, Russell griffiths said:

As far as I’m aware your smallest I joist would be 195mm so a bit bigger than your solid timber, and these will be a pain to fit pir into 

 

But two 100mm layers of 100mm Frametherm 35 would go in there nicely.

[osmononame]

Would the centres still be 600mm with the I-beams? Better decrement delay does have its appeal but I don't want to go looking down this road unless the costs are somewhat comparable. Can anyone chine in on that front? It looks like the frametherm is cheaper that PIR so there is savings there I think?

[Jeremy Harris]

Depends on the structural requirements.  Our twin-stud walls are all on 400mm centres, with the 300mm cavity being filled with blown cellulose.  The cellulose gives a pretty dense wall, that attenuates sound very well, as well as giving a reasonable U value, about 0.12 W/m².K.  The decrement delay is also fairly long, long enough to help give the house a thermal time constant of significantly longer than a day.

[Russell griffiths]

My I beams 225x 75 were double the price of solid timber, but the benefits could be well worth the extra cost. 

 

If you use 145 solid timber you have got to add extra insulation 

if you go with a wider I joist you can get more cheaper insulation in instead of the expensive pir. 

 

Lots of lots of sums to to do and at the end of the day you just have to make a choice. 

[Gone West]

3 hours ago, osmononame said:

Would the centres still be 600mm with the I-beams? Better decrement delay does have its appeal but I don't want to go looking down this road unless the costs are somewhat comparable. Can anyone chine in on that front? It looks like the frametherm is cheaper that PIR so there is savings there I think?

I have a 350mm portal timber I-beam framed house where the standard spacing is 600mm centres but because it's a portal frame this does vary. Our frame is insulated with Icynene spray foam and with external Rockwool insulation gives a U vaue of 0.095W/m2K. You have to consider whether decrement delay is of much interest which will depend on where you live. The climate and micro-climate of your site will determine the importance of decrement delay to your build as will the rainscreen materials and wall construction. We live on a relatively open site near the sea and as a result there is at least a breeze every afternoon and there is very little surface heat build up.