i-stud timber frame

[bissoejosh]

Having gone off SIPS for a variety of reasons I had hoped to use an i-stud system for the timber frame element of our build. One attraction is the lack (or reduction) of thermal bridging which hopefully eliminates the need for an external layer of insulation - keen to avoid celotex or similar if possible and keep things breathable. This simplifies the build and gets it weather tight that bit quicker - important for our DIY fit out.

 

I also have a preference for flexible insulation as it will also be a DIY job - a 220mm istud full filled with 0.032 glass batts looks to give 0.12/0.13 U value which is better than my target at an acceptable wall thickness.

 

Unfortunately none of our local timber frame firms seem to do i-stud frames which surprised me. Other than Touchwood (quoted - v.expensive) does anyone have a recommendation for an istud supplier? We're in Cornwall. Alternatively how badly would a 190 or 215 solid timber frame suffer from cold bridging and if the answer is badly what level of external insulation would be need to avoid the problem?

 

As always, opinions / alternatives welcome!

 

 

 

 

[Jeremy Harris]

Have you looked at MBC twin stud?  They use pumped cellulose insulation (recycled newspapers), the details are here: http://mbctimberframe.co.uk/

 

Edited June 18, 2017 by JSHarris

[ProDave]

Our build is 195mm studs with 100mm wood fibre board then render on the outside.  What external finish are you planning to have?

 

You definitely can build a frame out of I beams, a friend is building just like that near me using JJI I beams. I would have thought any builders merchant could supply them but you will need a structural engineer to sign off the design.

 

For insulation between the frame members I recommend Knauf Frametherm 35. A lot less horrible to handle than most glass wool type insulation and rigid enough to stay put with no slump even when insulating a 45 degree roof.

[bissoejosh]

2 hours ago, JSHarris said:

Have you looked at MBC twin stud?  They use pumped cellulose insulation (recycled newspapers), the details are here: http://mbctimberframe.co.uk/

 

 

I've seen the MBC system and would be very tempted if our build were simpler. My understanding is they only do full builds and we have a lower GF built separately for a variety of reasons. Certainly looks a great product in the right situation however. I was hoping i-stud might prove a decent compromise between a standard frame and something like the MBC.

 

2 hours ago, ProDave said:

Our build is 195mm studs with 100mm wood fibre board then render on the outside.  What external finish are you planning to have?

 

We've got a mixture of render and cladding, both on vented cavity but no outer block / brickwork much like yourself. I've seen the frametherm, infact I think I priced either this or dritherm so good to hear it's nice to use. I suppose using an engineer and sourcing direct could work for the frame, although I'd still prefer to outsource as a whole if possible. Did you specify 100mm externally for a specific reason or was that set by the overall wall thickness? Just wondering if we went for a conventional frame what would be the minimum external insulation needed to avoid issues with condensation/cold bridging.

[ProDave]

I was aiming for the same sort of overall thickness of wall as a "normal" timber frame. I had already concluded that leaving a 50mm cavity then 100mm blockwork was a very expensive rain screen that adds very little to the insulation as that cavity has to be so well vented so is open to cold air. So my designer came up with the established wood fibre and render cladding system, and a thicker frame to fit more insulation. Overall U values allowing for the cold bridging of the frame 0.14

 

This document shows how to use wood fibre cladding with either timber or render finish http://www.greenspec.co.uk/downloads/?filename=pavaclad1.pdf

 

I was originally going to use a form of blown in insulation, but changed to using the frametherm when I found it was half the price, gave the same U value, and was a DIY job.  Because of the frame make up with the OSB racking layer on the inside (lots of people tried telling me I had put the fame up inside out) the frametherm insulation went in from the outside as I clad the walls in the wood fibre board, doing one wall at a time and getting it rendered before moving on.

[jack]

14 hours ago, bissoejosh said:

I've seen the MBC system and would be very tempted if our build were simpler. My understanding is they only do full builds and we have a lower GF built separately for a variety of reasons. Certainly looks a great product in the right situation however. I was hoping i-stud might prove a decent compromise between a standard frame and something like the MBC.

 

MBC built a house on top of @Bitpipe's separately constructed basement.  Is that the sort of thing you're doing?

[Bitpipe]

5 hours ago, jack said:

 

MBC built a house on top of @Bitpipe's separately constructed basement.  Is that the sort of thing you're doing?

 

Correct

 

We replicated the concrete / EPS detail that MBC rely upon for their twin wall system and it all worked fine. We worked off drawings initially but I made them come measure the actual basement before going into production - caused a few weeks of delay but gave peace of mind.

 

The challenge you will have is ensuring that the non MBC elements are sufficiently airtight (our basement is a big waterproof concrete box so no worries there for us). 

 

Suggest you give them a call for a chat, I know that they've done at least one other 'hybrid' build in the past. 

[dimpsy]

Could try these guys http://alltimberframes.co.uk  not too far and do an i-beam stud.

 

 

[bissoejosh]

22 hours ago, dimpsy said:

Could try these guys http://alltimberframes.co.uk  not too far and do an i-beam stud.

 

 

Excellent, will get in touch with them...

[bissoejosh]

On 19/06/2017 at 11:25, Bitpipe said:

 

Correct

 

We replicated the concrete / EPS detail that MBC rely upon for their twin wall system and it all worked fine. We worked off drawings initially but I made them come measure the actual basement before going into production - caused a few weeks of delay but gave peace of mind.

 

The challenge you will have is ensuring that the non MBC elements are sufficiently airtight (our basement is a big waterproof concrete box so no worries there for us). 

 

Suggest you give them a call for a chat, I know that they've done at least one other 'hybrid' build in the past. 

Sounds interesting, yes although ours isn't a basement in the sense of being below ground it has a lot of similarities. The detail at the join is crucial and already causing a few headaches but I'm confident we can sort it.

 

I'll get in touch with MBC and see what they say.

[Simplysimon]

@bissoejosh just catching up on a few posts as been off forum for a while, i'm doing a jjii beam stud wall and roof of 350mm. as i'm a joiner and teach, i was concerned about cold bridging, insulation, airtightness and ventilation. going down the passive route to avoid these problems. kit is designed and should be signed off by ser this week. i'm building the kit myself as i've got a shed to build it in

i had originally thought of twin stud, but reckoned jji an easier option, had thought to manufacture the jji but reckoned that getting them tested and signed off would be too much hassle.

 i would also look at different options for insulation as this is one of the biggest problems of cold bridging, we're going down the route of pumped cellulose to avoid gaps.