Self build dream (nearly!) beginnings

[Jeremy Harris]

10 hours ago, LA3222 said:

So, what I take from that is a twin stud is different (as I already knew).  But a 140mm stud frame (The majority of TF) sits on a 140mm soleplate in the same way that a SIP panel does - so the problem applies equally to both?

 

There is no inside/outside member for 140mm stud so it is no different to SIP sitting on a 140mm sole plate.

 

So when you comment about SIP being subject to interstitial issues it is misleading as the wording implies this applies to SIP and not others when in reality it applies to most TF structures?

 

 

The key thing is that SIPs wall panels have the vertical structural loads spread equally between the inner and outer OSB skins, so need these loads to be taken equally into the foundation.  A timber frame can be designed to place all the vertical loads towards the inside face of the frame, so alleviating the need for any support under the outer face.

 

The thermal bridging issue is just one of how best to keep both SIPs skins adequately supported, without creating a thermal path from inside to outside through the supporting structure.  There are options available to do this, it just needs a bit of careful detailing, that's all. 

 

A 140mm timber frame will need additional insulation just to meet building regs, so adding this on the outside removes the problem.  The same can be done with SIPs, and this was the option I wanted to use when we were originally going to have a SIPs build (we only didn't because the SIPs builder's prices were higher than we would have liked, and they were really slow to respond at the time).

[LA3222]

39 minutes ago, JSHarris said:

A timber frame can be designed to place all the vertical loads towards the inside face of the frame, so alleviating the need for any support under the outer face.

How do you do this with a 140mm stud wall?

[Jeremy Harris]

2 minutes ago, LA3222 said:

How do you do this with a 140mm stud wall?

 

Place the 140mm stud on the passive slab ring beam and add external insulation.  A 140mm stud wall will almost certainly need more insulation added, both to get the wall insulation up to a reasonable value and to mitigate thermal bridging through the studs, so the external insulation layer can just extend down over the floor - wall junction and mitigate any thermal bridging at the base, too.

[LA3222]

16 minutes ago, Bitpipe said:

I found summer much more unpleasant as the caravan got uncomfortably hot very quickly in direct sun

Ha, ^this ^.

 

The summer has been honking in the van, to the extent that I spent £350 on an aircon unit.  It's not entirely effective as I had to MacGyver the outlet pipe onto on of the vents along the bottom of the van so some of the hot air leaks back into the van and the pipe gets bloody hot further bringing heat back in.  But it does make a difference at lowering the temp down a few degrees but it needs to be used sparingly.

 

I have a dehumidifier on the go 24/7 to try and eliminate dampness.  The van came with wall panel heaters in every room and I bought another couple to go in the lounge and missus room.  The kids share so their room gets hot.

 

Once the house is built it will be strange having so much space again!

[LA3222]

12 minutes ago, JSHarris said:

 

Place the 140mm stud on the passive slab ring beam and add external insulation.  A 140mm stud wall will almost certainly need more insulation added, both to get the wall insulation up to a reasonable value and to mitigate thermal bridging through the studs, so the external insulation layer can just extend down over the floor - wall junction and mitigate any thermal bridging at the base, too.

So can we agree that the soleplate issue exists for all TF construction bar Larson truss type methods.

[Jeremy Harris]

10 minutes ago, LA3222 said:

So can we agree that the soleplate issue exists for all TF construction bar Larson truss type methods.

 

 

Not really, it varies on several factors, not least being the heat capacity and thermal conductivity of the type of construction.  A low heat capacity structure will respond very differently to dynamic changes, particularly in the external layer, than a high heat capacity structure, for example.   @PeterStarck's build uses an I beam portal frame on a passive slab,  so he also had to ensure the detailing was right around the floor - wall junction.  This may have been easier, as I beams are probably better able to transfer vertical loads from the outer member to the inner one via the OSB web, so reducing the load that the outer member applies to any supporting structure.  I can't recall offhand how he did this, but have a feeling that the outboard side of his frame bears on an EPS upstand, a bit like ours.  Perhaps he could give some input if I have this wrong.

[Bitpipe]

35 minutes ago, LA3222 said:

Once the house is built it will be strange having so much space again!

 

Certainly is - ours sprouted into teenagers shortly after we moved in and we didn't see each other for months  

[LA3222]

1 hour ago, JSHarris said:

the outboard side of his frame bears on an EPS upstand, a bit like ours

The outside skin of my sip panel rests on an EPS upstand so what gives?

 

I give up - you can't/won't see that the point I am trying to make is when you talk about sole plate issues you speak as if it is a SIP only problem and a negative against that particular method of construction. The way I see it, a soleplate is a soleplate, so with SIP or 140mm stud wall you have the same issue. 

 

The difference lies with timber construction which have the loading on an inner member such as Larson truss (being the most common as that is what MBC use for their passive construction) - but I am not talking about them.  I am talking about 140mm stud walls and SIP.

 

I think the wording of your advice regarding SIP is at times misleading in that the issues you raise are not unique to SIP but your wording perhaps can be construed as implying that.

[LA3222]

43 minutes ago, Bitpipe said:

 

Certainly is - ours sprouted into teenagers shortly after we moved in and we didn't see each other for months  

I think the girls will like that - they have established a rule where only one of them can be in their room at a time at the minute (bar sleeping!).  After a couple of years of this I am sure they will appreciate the space!

[jamieled]

Following this with interest! We have an I beam frame sitting on a 300mm wide sole plate sitting on a passive slab. I'd say around 20% of the sole plate sits on an eps upstand, the rest on the insulated slab.

 

Looking at it from a relatively uneducated perspective I'd have thought the load is spread through both timber flanges of the I beam, but maybe not.

[Jeremy Harris]

16 minutes ago, LA3222 said:

The outside skin of my sip panel rests on an EPS upstand so what gives?

 

I give up - you can't/won't see that the point I am trying to make is when you talk about sole plate issues you speak as if it is a SIP only problem and a negative against that particular method of construction. The way I see it, a soleplate is a soleplate, so with SIP or 140mm stud wall you have the same issue. 

 

The difference lies with timber construction which have the loading on an inner member such as Larson truss (being the most common as that is what MBC use for their passive construction) - but I am not talking about them.  I am talking about 140mm stud walls and SIP.

 

I think the wording of your advice regarding SIP is at times misleading in that the issues you raise are not unique to SIP but your wording perhaps can be construed as implying that.

 

 

Not just a SIP issue at all, but still one that applies to SIPs when used with a passive slab, as it does to other timber frame construction methods on a passive slab.  The example I quoted of @PeterStarck's build, which uses foam-filled I beams has potentially the same issue at the sole plate, which is why I speculated as to how this might have been overcome.  I can't recall the detail, but think he used an external insulation layer to address it, much the same as Kingspan agreed was a good solution for SIPs in this particular type of construction.  Other solutions are to use insulated load bearing materials, like foamglas, to reduce thermal bridging (pretty sure this may be a standard detail from some SIPs suppliers).

 

As long as the floor-wall detail is designed carefully then I can't see there's any problem, but there are certainly examples of some SIPs builds where this detail has been poorly thought through.  It's a potential issue that came up in a thread on Ebuild, where examples were given of wall-floor junctions for SIPs construction that were potentially iffy, in that thermal bridging just hadn't been adequately dealt with in the design.  The same is true for early timber frame builds - who can forget the disasters from early English timber frame builds in the 1970s and 80s that rotted out due to a failure to understand interstitial condensation risk.  A former colleague bought one of these 1970's timber frame houses, built by Barretts, IIRC, and ended up having to have the external walls replaced after a few years due to rot.  The problem was that they had built the walls with the sole plate bearing on a cold foundation and had failed to provide adequate vapour control.

[Jeremy Harris]

24 minutes ago, jamieled said:

Following this with interest! We have an I beam frame sitting on a 300mm wide sole plate sitting on a passive slab. I'd say around 20% of the sole plate sits on an eps upstand, the rest on the insulated slab.

 

Looking at it from a relatively uneducated perspective I'd have thought the load is spread through both timber flanges of the I beam, but maybe not.

 

Thanks, that seems entirely sensible to me, as that EPS upstand should significantly reduce the potential problem.

 

I also think you're right about the way loads are better able to be transferred through the  OSB web of the I beam from one member to another, with the web being able to take significant loads in shear.  I beams are different to SIPs in this respect, as the SIP manufacturers are usually fairly clear that the foam core should not be relied upon to take sustained shear loads (sustained being, I think a key point, as I believe their concern may be about long term creep and possible delamination of the skin - core bond).   That's why they usually seem to require that both edges of the panel have adequate structural support at the base, as the skins are bearing the vertical load (which is  unlike pretty much any other timber frame construction method).   I'd guess that there maybe other ways to transfer the load from the outer skin to a point inboard of it, so allowing insulation to lie under the outer part of the panel, but it's still a detail that needs care to work through.

[Bitpipe]

One design detail to be aware of with a MBC style construction vs other TF or SIPs is the ability of the outer skin to take a fixing - i.e. from battens for renderboard or cladding.

 

I understand that standard TF or SIPs outer panels are made from OSB or equivalent which will take a fixing, although ideally the fixings should target structural ribs behind the outer panel itself.

 

MBC use a lighter weight Panelvent board, similar to MDF which does it's job perfectly but cannot be relied to take an external fixing - these MUST go into the structural ribs which are marked out on the building paper with tape or staples.

 

Our render system has issues as the render board battens did not always line up with ribs and where they went into only the skin, they came away leading to bulging. All needs to come off and be replaced to remedy.

 

Note that the airtight layer is mostly on the inside (it does come to the external panel between floors) so such fixings should not compromise it.

Edited September 18, 2019 by Bitpipe

[LA3222]

1 hour ago, JSHarris said:

I'd guess that there maybe other ways to transfer the load from the outer skin to a point inboard of it, so allowing insulation to lie under the outer part of the panel

My foundation plan designed  by TSD has the sole plate straddling the insulated slab and an insulation upstand.  So in effect the inner skin is over the concrete and the outer skin is sat over EPS.

 

As to all the above, I don't disagree with the content of what you say @JSHarris, I was simply trying to say that your comments at times seem to describe a SIP only issue which is not the case, so was just trying to clear that up.

[Jeremy Harris]

2 hours ago, LA3222 said:

My foundation plan designed  by TSD has the sole plate straddling the insulated slab and an insulation upstand.  So in effect the inner skin is over the concrete and the outer skin is sat over EPS.

 

As to all the above, I don't disagree with the content of what you say @JSHarris, I was simply trying to say that your comments at times seem to describe a SIP only issue which is not the case, so was just trying to clear that up.

 

 

It is a specific SIP issue in the context of this thread, though, as the OP is planning to build with SIPs, so needs to check and make sure that the wall-floor detail is properly designed.  My comments were not directed at you, but to the OP, and anyone else that is using SIPs that is not aware of this potential issue. 

 

The reason for highlighting this is that it was clear from the thread on Ebuild that there were some people designing foundation details for use with SIPs that were not aware of the potential problem.  You used an SE (same one I used) that is very familiar with the potential issues, so designed them out, but that doesn't, by any means, imply that all SEs are as clued up about this (the evidence presented in that other thread suggests that few were).

[Simplysimon]

20 hours ago, SuperJohnG said:

Thanks @Simplysimon what sort of stage are you at? 

currently the kit is in the process of being built, getting there, slowly

[Gone West]

On 18/09/2019 at 11:09, JSHarris said:

Not just a SIP issue at all, but still one that applies to SIPs when used with a passive slab, as it does to other timber frame construction methods on a passive slab.  The example I quoted of @PeterStarck's build, which uses foam-filled I beams has potentially the same issue at the sole plate, which is why I speculated as to how this might have been overcome.  I can't recall the detail, but think he used an external insulation layer to address it, much the same as Kingspan agreed was a good solution for SIPs in this particular type of construction.  Other solutions are to use insulated load bearing materials, like foamglas, to reduce thermal bridging (pretty sure this may be a standard detail from some SIPs suppliers).

Sorry I haven't replied earlier, I haven't been on the forum for a couple of weeks. Our I-beam sole plate sits entirely on the concrete slab with the OSB3 racking lining up with the edge of the concrete. There is an EWI layer of high density RW6 Rockwool on the outside of the OSB3 which joins up with the EPS foundation upstand.

[Eileen]

Back to the OP - we used 4Wall SIPS from Tribus for the main construction of our Passivhaus. As ex-timber frame guys who now manufacture the 4Wall panels, they did everything from the slab upwards (not including the slab itself), so SIPS panels; stud-walls, floor and roof timbers ready for the insulation and membrane. Their speed caught our builders by surprise because first-fix was upon them before they knew it. They're based down here in Devon but have built in Scotland.

 

[SuperJohnG]

I wanted to sort of close the loop on this thread and provide an update after 6 months of membership here. 

 

I've now completed purchase of the plot and finalised design of our house, it has taken 5 months to complete purchase of the plot and about 2-3 to design the house. I've done a but of an update on the design and more can be found here: