SIP vs CPS

[Kelvin]

We are still deciding which way to go in terms of the kind of house we want to build. We love the HebHomes Longhouse style and we think this style of house will suit our plot very well. HH do three timber kit variants. Closed panel, SIP, and CLT. The closed panel system was cheaper (still is on their website) but may end up being similar to a SIP construction. I’ve read a lot about SIP construction and I am having doubts about using it. I also get the impression it’s not favoured on here.
 

We are now leaning towards their CPS kit. Does CPS suffer the same risks as SIP construction regards mould and rotting of the OSB? 

[scottishjohn]

rotting of any wood structure is down to how its built ,nothing else .

to have mould you must have water ingress 

[Kelvin]

Yes well that was my view too but SIP does seem to split opinion. I guess some of that might be because it’s less common in the UK.

[A_L]

1 hour ago, scottishjohn said:

to have mould you must have water ingress 

 

or condensation

[scottishjohn]

10 hours ago, Kelvin said:

Yes well that was my view too but SIP does seem to split opinion. I guess some of that might be because it’s less common in the UK.

main horror stories  seem come from roofs where people have laid directly onto the house wrap + sips ,

instead of having  house wrap then  a ventilation gap(batons) and then roofing  

or direct renndering onto sips  

again instead of having a breathing gap  or a gap and cladding 

you need a ventilation path in any wood framed or sips house 

 my own 1979 tf house has brick outer skin ,but thecavity wall is connected to under the house and the roof is a ciold type 

so draft comes from under floor up between the brick and wood wall ,then up into the loft and out of soffit vents 

 

i tried blocking top of cavity walls 10 years ago  and in one winter the plywood roof sarking went black  on north side of house -- removed the insulation that was blocking the cavity and it all disappeared 

 that proved to me you need a direct ventilation path

as they had in old stone houses with lathe +plaster 

-seal it and form of condensation or moisture will cause problems over time 

 

[markocosic]

I wanted to draw a design, have it made accurately, then plonk it onto foundations with no mucking about on site.

 

Call it a over reaction to having had to deal with badly built brick houses where nothing is square or level and you're forever mucking about making things fit well.

 

The more I read on SIPs the less they made sense though. The vapour resistance of the outside is the same as the inside. (Both OSB) The weak paths are the joints. Any airflow or vapour movement through that structure is going to go through the joints. The worst place to have moisture in OSB.

 

If you're VERY good on air tightness - assembling carefully and adding a membrane to the inside of the SIP that you're religious about protecting - and you build a secondary structure outside the SIP (battens,  breathing membrane, battens, cladding of some kind) then they work.

 

Price that up and you might as well panel build or even stick build though; and if you go for those routes then you ends up with a structure that's far more resilient to minor f**kups and viable to repair too.

 

The better SIP vendors even said as much. "Our price is supply and erect and includes battens, membrane, and battens over the sip. In the early days we did supply only but people always screw up airtightness, the ridge always rotted first (highest driving pressure for moisture from inside/hardest to fit up tightly), and we got fed up of the warranty claims. If anybody says you can render the outside directly and bash some shingles on top then run a mile!" (or words to that effect)

 

 

Advantage of the SIPs was speed. (up and watertight in days)

 

We found some framers who were framed, insulated, and watertight in 5 weeks. (and built in snow season rather than rain season)

 

If the choice was panel or sip then panel every time.