SIP's Construction Panels, anyone used them?

[villageidiot]

I am adding a flat roofed extension on top of a garage and considering using SIP panels , anybody have any experience of this construction method or any disadvantages that I may not be aware of ?

[toohuge]

I've not used these in a building yet, but I have researched these quite a bit....

It does sound like SIP's would be suited to such an extension, they offer excellent insulation and very fast build times. My main gripes with SIP's is the amount of wood used in these panels - we live in the US and termites are a serious issue, not so in the UK.

I am guessing that you will be using SIP's for the roof too? That would give a very well insulated envelope.

[villageidiot]

Yes , the intention would be to use it for the roof as well.

[moles]

http://www.pistonheads.com/GASSING/topic.asp?h=0&a...

[villageidiot]

Cheers Moles

[anonymous-user]

We used SIPS for our extension. Brilliant method of construction. Going to do the mancave in SIPS too - full build including roof. More info on the blog (have a look at the other Nov entries) http://themeadenproject.wordpress.com/2012/11/08/8...

(still skint) emma

[Onemcs]

I've used them a few times on large scales.

Great thermal performance
Can speed up programme if procured early
Quicker to water tight which is always important

I also wrote a dissertation on them for my degree. Worked out similar costs and a better option to alternative methods, as long as you order them early enough!

Edited by Onemcs on Friday 24th October 13:41

[toohuge]

Op, what concerns do you have?

My only concern when building a tight envelope is appropriate ventilation and humidity control...

[villageidiot]

As this would be an extension to a 1980 built home it had been suggested that the insulation would be far superior to the existing property and this could cause problems ??, I plan to improve the insulation in the rest of the house but may struggle to get close to the performance of the SIP's. Another concern was that is does not appear to be widely used , is there a reason for this ? it sounds almost too good to be true with no drawbacks other than the insulation compatibility when used for extensions.
P.S. I have no building experience personally other than having a garage built which this extension will be above.

[toohuge]

villageidiot said:

As this would be an extension to a 1980 built home it had been suggested that the insulation would be far superior to the existing property and this could cause problems ??, I plan to improve the insulation in the rest of the house but may struggle to get close to the performance of the SIP's. Another concern was that is does not appear to be widely used , is there a reason for this ? it sounds almost too good to be true with no drawbacks other than the insulation compatibility when used for extensions.
P.S. I have no building experience personally other than having a garage built which this extension will be above.

Correct - the insulation in the rest of the house will not be anywhere near that of the SIP's, especially with the SIP roof too. These are very, very well insulated. As I mentioned above, ventilation and air circulation need to be thought out well, but a mini split ac unit could be a good idea....

I find that a lot of builders don't like new technology - that's the same with every new type of wall system out there. For example, here in the US, people are still building stick and frame (wood) despite the humid climates, dry rot and termites - yet still don't like the idea of using any other wall system.

I would be surprised if using SIP's would cause any major issues with the rest of the home.... in many homes, areas such as a garage are not as well insulated yet these can be attached to appropriately insulated main structures but we don't see huge problems there

[MintSprint]

villageidiot said:

...other than having a garage built which this extension will be above.

I'm Design & Technical Manager for a company that designs and manufactures buildings in SIPs (and conventional timber frame, and traditional oak frame; in fact, if it's in timber, we'll build it for you... though we haven't done CLT yet, 'cos I'm still struggling to figure a technical justification for it, or find a project that lends itself).

What is the construction of the garage you'll be using as a base?

We've done lots of upper floor extensions.

Biggest problems are getting everything to fit accurately (particularly with SIPs, which isn't as straightforward to 'fudge' on site as conventional timber frame) on top of the 'base', and the detailing of the junction between the structures to prevent damp/water ingress... but I'm talking about structures that are probably a lot more complicated and dimensionally inaccurate than yours. In very basic terms, you need to establish a wallplate that is nice and accurate in both line and level (we normally specify +/-10mm on line and +/-5mm on level as target figures), and once you've done that, it's easy! You have to remember, though, that SIPs (and most conventional timber frame in this country) are factory manufactured to millimetric tolerances on drawings that have been prepared in advance, so it's very much a case of measure thrice, cut once, if you want a smooth erection on site.

I'm in the middle of erecting a new upper floor (albeit in conventional timber frame, though there's not much difference in approach) on top of an old cottage in Wales, where the ground floor masonry we're building on was all over the place - the amount of effort it took to get it straight and level enough to erect the timber frame onto would have probably made it more cost-effective to level the whole lot and start again, but that has been probably the worst scenario I can imagine encountering and it's still gone relatively smoothly (a lot better than I expected, in fact).

As Toohuge says, you need to be conscious of both internal damp problems and air quality problems if you have a very airtight structure - on a new build, we would always recommend MVHR where we're aiming at a design airtightness figure of 3.5 m3(h.m2) or less (which is easy to achieve with SIPs), but I'd be inclined to take a more pragmatic approach than going to the expense and complication of fitting a mini A/C unit in a garage extension.

SIPs is a good system, but it's advantages are probably slightly exaggerated; it's a fashionable 'fad' amongst self-builders at the moment, because the technical novelty and apparent simplicity appeal to many, but the reality is that it costs more than both masonry and conventional timber frame, and the technical advantages are eroded by various other issues when you dig a bit deeper. It's still probably a good choice for what you have in mind, however.

Edited by MintSprint on Friday 24th October 23:20

[villageidiot]

The garage is block built with insulated cavity and is currently warmer than the house which has a mansard roof with no insulation either above or to the sides . The only insulation is in the walls on ground floor which had polystyrene beads injected .

[MintSprint]

villageidiot said:

The garage is block built with insulated cavity...

With what internal/external leaf thicknesses and what cavity width (and do I understand correctly that the garage cavity wall is fully filled with EPS bead insulation)?

The straightforward approach is to make the SIP panel the same thickness as your inner leaf, so that it just sits on top of the wallplate and lines through (though if you've got a 100mm blockwork inner leaf, the U-vale of a SIP panel of equivalent thickness isn't going to be as extraordinary as all that... a 100mm thick SIP panel with 2x12mm skins and 76mm. of PIR insulation as its core will only give you a U-value of about 0.27, which is nothing to write home about, these days).

Then you need to think about what sort of external cladding you're going to use for the upper structure, and how it will line through (and work in terms of DPC's and cavity ventilation, if required) with the outer face of the structure below.

If you're intending to continue the masonry outer leaf upwards to form the external cladding (though this would partially defeat the object of using a SIP structure), remember that the cavity on any SIP or timber frame construction will need to be ventilated... so if your existing cavity is fully filled with insulation at ground floor, you're going to have to work out a detail to close it at wallplate level, with a DPC/cavity tray, and ventilate it above. You then have a potential cold bridge, where the insulation changes position from being within the cavity, to within the SIP panel.



All do-able, but the devil is in the detail.


Edited to add: ignore the comment about cold bridging: I was talking bks after a long day and too much wine! The garage below will effectively be an unheated space, of course, so cold bridging is not an issue!

Edited by MintSprint on Saturday 25th October 07:41

[akaAlso]

If you sit the timber frame/ sips panels on top of the new floor joists this then allows a free choice of panel width. (Platform construction)

[villageidiot]

The garage is built with what looks like breeze block laid on its narrow side , the cavity looks to be about the same width as one block and is filled with rigid insulation board, the garage was built 6 years ago . It's just the house which has the bead insulation.

[MintSprint]

villageidiot said:

The garage is built with what looks like breeze block laid on its narrow side , the cavity looks to be about the same width as one block and is filled with rigid insulation board, the garage was built 6 years ago . It's just the house which has the bead insulation.

Grrr....

You have heard the saying 'garbage in = garbage out'?

Detailing is important with SIPs, and as the name suggests, it's about detail.

You are going to have to be very clear about your existing construction if we are to give you valid advice on how to deal with it.

• What is the outer leaf? Brickwork? Rendered blockwork?
• What thickness is the blockwork inner leaf (I'm expecting 100mm, but you can get different thicknesses of 'breeze block')?
• Is the cavity really 'filled' with rigid insulation board, or have you got, say, 50mm of insulation board and 50mm ventilated cavity?
• As above, what is the width of the cavity; if it's 100mm blockwork, then 'about the same width' (100mm) would have been a hell of a wide cavity for something built 6 years ago, if the cavity is then 'filled' with insulation board (and especially on a garage, which doesn't really need insulating). We're only just needing to build 100mm fully-filled cavities now, to deal with the latest generation of Building Regulations that came in in April of this year.
• What do you intend the external cladding of the extension to be?

(P.S.: see my edit above about thermal bridging: not an issue if you're above an unheated space)

[villageidiot]

Ok, I've just measured , blocks are 100mm and overall width is 275mm inc render so cavity is probably actually about 50mm, the finish of the extension will be rendered to match existing garage and house . The attached computer generated photo shows what we are building , it is what you see above the wall to the left side , the

[MintSprint]

I have to say that I'd be inclined to build that in masonry, if I were you. The complications of building it in SIPs would take more effort to resolve than they're worth, IMO.