Truly DIY SIP construction…

[SteamyTea]

2 hours ago, Iceverge said:

By keeping a layer of continuous insulation outboard of any organic materials like timber then it will remain above the dew point for almost all of the year and condensation cannot happen

Yes, that is the primary defense against condensation, keeping above the dewpoint.

Also spreads out any cold bridges.

 

2 hours ago, Iceverge said:

I would argue that absolute humidity tends to equalise rather than travel in any particular direction

It does diffuse, and quite rapidly, but it also follows any temperature gradient.

 

I was trying to set up a couple of IR thermometers to log wall surfaces, because I have noticed that my inner walls are a couple of °C lower than the ambient temperature, and the outer wall a couple of °C higher than OAT.

Probably why there is a default R-value for the air film.

I keep meaning to research this whole area more, but I need to feed the starving Emmets and we are getting busier as summer approaches.

[G and J]

As for our main loft we’re thinking a cold loft, with lots of insulation laying on the plasterboard of the ceilings.  
 

We have limited headroom due to the ridge height being restricted and I hate chamfered rooms (are they known as dropped eves?) and so the loft is only good for solar pv kit and storage, and having cleared our previously overloaded with tutt loft where we now live we’re determined not to store stuff up there.  
 

I think a cold loft is the simplest and quickest and cheapest way of doing it, but when I get round to it I’ll weigh up cost and function of a warm loft too.  Especially if it has no affect on room heights.  

[G and J]

On 08/06/2024 at 10:17, G and J said:

I’ve not spoken with an ICF company or a concrete delivery company but the fact that the boom would have to arch over electric cables would be a worry.  My target is a total wall thickness of ~300mm (inc. 70mm of battening and cladding on the outside skin) and I’m under the impression that ICF would struggle with that.  
 

Stick built is the default option, I’m exploring alternatives in part as a validation exercise but I’m learning tons along the way.

 

My investigations so far indicate that a SIPs on site blank panel build would use 175mm PU SIPs or 200mm EPS SIPs to yield a u value of better than 0.17.

 

Cost wise, and this is very broad brush, (and includes walls, joists, chipboard flooring at first floor only), it appears that:

 

1. Get a company in to do the lot and it’s just over 100k.  Game over.

2. Have a different company make it in factory and deliver it for me to erect and it’s about 52k.

3. Buy blank PU SIP panels and build it myself, buying in joists etc. from other suppliers will cost about 35k.

 

Each of these options require a fire board skin, cladding, internal battening and osb/plasterboard (I want good solid walls).

 

So, next step is to repeat the same process for stick built.  At present I’m struggling to work out a stick built wall build up that yields a decent u value and the right thickness.  

Well, I thought I’d feed back on all my investigations.  Revising my earlier SIP figures, to include a cement board skin, the costs for the frame, not including barrier membranes, battening, cladding, PB or skim, roof trusses, and in the case of the SIPs, also excluding the attached garage (no idea why, but they all left this off):

 

1. Get a company in to do the lot and it’s just over 104k.  Game over.

2. Have a different company make it in factory and deliver it for me to erect and it’s about 56k.

3. Buy blank PU SIP panels and build it myself, buying in joists etc. from other suppliers will cost about 39k.

4. Stick build it (excluding labour), assume cement board skin and osb3 skin, 140mm rockwool in frame, 50mm PIR inside that, 18k.

 

Crumbs.  I think my way forward is clear then….

[JohnMo]

6 minutes ago, G and J said:

4. Stick build it (excluding labour), assume cement board skin and osb3 skin, 140mm rockwool in frame, 50mm PIR inside that, 18k

Bonkers the difference in price, that's why I went DIY. A friend helped out, I insisted he got paid for all hours worked, so it was a job and we worked an 8 hour day Mon-Fri. He worked as a pair of hands and we bounced ideas of each other. Took about 4 weeks to build all external walls (70m x 3m).

[G and J]

2 minutes ago, JohnMo said:

Bonkers the difference in price, that's why I went DIY. A friend helped out, I insisted he got paid for all hours worked, so it was a job and we worked an 8 hour day Mon-Fri. He worked as a pair of hands and we bounced ideas of each other. Took about 4 weeks to build all external walls (70m x 3m).

It accounts for how all the high energy hard sell is paid for for the SIP providers.  I’m guessing the same is true for frame kit providers too.
 

In our case the fire resistance requirements put SIPs at a disadvantage but I think that there simply isn’t a mature market for blank SIP panels like there is for other building materials, otherwise the cost of a SIP self build would be closer to stick built.  With markets, volume is such a dominant factor.  
 

I think you’ve shared your wall build up before JohnMo, but I can’t find it.  Would you mind sharing it again?

[JamesP]

As you might be on a stick build journey, I have included my wall / roof build drawing (Hand drawn) and a few photos.  About 275sqm, took a while to get weather tight but very much the most satisfying part of my self build and it is square!

 

Wall : Roof details-1..pdf

[G and J]

8 minutes ago, JamesP said:

As you might be on a stick build journey, I have included my wall / roof build drawing (Hand drawn) and a few photos.  About 275sqm, took a while to get weather tight but very much the most satisfying part of my self build and it is square!

 

Wall : Roof details-1..pdf 777.43 kB · 3 downloads

Goodness, thank you for sharing that.

 

So your OSB skin is on the inside and is your main airtight layer in your wall.   Not sure we can go that route due to fire resistance - I’m still not sure how I do address airtightness. 
 

Your framing timbers are I’m guessing circa 5.1m and your floor is hung from the side of them.  Was there a specific advantage in doing that over what I think is called a platform floor?  (I mean where you build downstairs, the floor sits on that and then you build upstairs directly on top of it.)
 

[JamesP]

Yes, the first floor built on top of ground floor.  Two timber stud spine walls on the ground floor to support the joists, GF was 13m x 7m.

The first floor timber joists were 44mm x 220mm x 4400mm + some glulams.

Vapour barrier behind the OSB, Pavatherm on the outside then batten, counter batten and cedar cladding.

 

[JohnMo]

1 hour ago, G and J said:

think you’ve shared your wall build up before JohnMo, but I can’t find it.  Would you mind sharing it again

That wasn't what we did in the end, but it gives a 0.1 U value

[G and J]

2 hours ago, JohnMo said:

That wasn't what we did in the end, but it gives a 0.1 U value

That’s a timber frame cavity wall, and an excellent u value to width ratio if I’ve understood it correctly.  May I ask why you didn’t do that?

[JohnMo]

25 minutes ago, G and J said:

That’s a timber frame cavity wall, and an excellent u value to width ratio if I’ve understood it correctly.  May I ask why you didn’t do that?

I went ICF.

 

It's more like a Larson strut, a structural frame (95x45) filled with insulation, then 50mm PIR glued to the structural frame, then a non structural frame 75x45,filled with insulation and a further layer of PIR.

 

Replace outer layer of osb with cement board.

[scottishjohn]

On 08/06/2024 at 12:03, G and J said:

You'd be surprised how the promised performance of a SIP wall worsens, once taking these all into consideration, as SIPS often require solid timber blocking in these areas.

I don,t see howthats any different to a stick build as you have more wooden upright -like every 16"  

where as you will only have spines every 48" if you use 4ft wide panels 

so you will have less wood in the sips 

 and if that is a problem to you, then  add anoutside insulation layer or use insulated palster board  on outer walls

early you were asking about window holes in blamk panesl 

simple --cut out hole rebate insulation back and fit wood inbetween the osb 

Edited June 14 by scottishjohn

[G and J]

5 minutes ago, scottishjohn said:

 

On 08/06/2024 at 12:03, G and J said:

You'd be surprised how the promised performance of a SIP wall worsens, once taking these all into consideration, as SIPS often require solid timber blocking in these areas.

 

 

Slander and calumny!  Such wisdom cometh not from me, that was from Iceverge.  It made sense to me but maybe I’m missing something. Again. 

[scottishjohn]

taking what you ssiad at the very beginning on acces and man power 

icannot see stick nuilding being easier for you and fitting the insulation in a stick build is very time consuming and you will end up with bits that are hard to get to 

solid panels at a suitable size will be easier for you i feel 

Icf contruction will leave you with much thicker walls ,which was alos a problem if memory serves.

I quite like ICF --but  with your restrictions   wall bracing hire ect  i would go sips ==

just my opinion --but everyone has one ==so its up to you in the end what seems simplest for you 

Edited June 14 by scottishjohn

[G and J]

I will readily admit I like the idea of SIPs and I did try really hard to assemble the best possible case for them.  However the result is not favourable.  
 

It’s worse in my case as I have to have a fire resistant layer on the outside.  The SIP companies I’ve consulted advise that that needs to be battened rather than fixed direct so that adds to wall thickness with little improvement in insulation.  It negates the width vs u value advantage PU based SIPs provide.  
 

Even without this the extra cost of SIPs is significant.  I think this is likely to be because there isn’t an active market in sufficient volume for what I would call diy SIP build, meaning from blank panels.  
 

I did find suppliers of technically suitable PU SIPs. (I focussed on PU SIPs as EPS SIPS yield a thicker wall given the above than stick built for a given u value.)  But it’s not like the supply of OSB3, there simply isn’t the competition.  The end result is I can source and have built for me a stick built frame for a lot less than I can source SIP panels for me to erect.  Yes, I then have to insulate but that’s ok with me. 
 

I’ve learnt a lot about SIPs in this process, and I remain shocked by the way the industry is so dominated by companies that sell hard and clearly have very pleasant margins.  I understand that even local building companies don’t build using SIP blanks, they get a specialist company to put up the kit and they take it from there. 
 

The supply is simply not there competitively (yet?)
 

I now have a high regard for SIP technology, and I’m grateful for inputs from enthusiastic proponents - it’s helped me enormously in my data gathering - but my numbers are what they are.  And as those numbers translate into Greggs sausage roll tokens (our build is just in walking distance - praise be!!) then those numbers guide me. 
 

My next research area should be diets, but it’s probably going to be warm vs cold roof and roof air tightness.   😕

[saveasteading]

20 minutes ago, G and J said:

have to have a fire resistant layer on the outside.  

This should be routine. Change spec from plywood or osb, to cement board. Do you have a plan?

 

My view us that sips gets specified by architects for schools etc, and isn't challenged so it's easy money. I've been confronted for 20 years by glossy mags telling me it's the only way. Some fall for it. You have not. For a while you were convinced by the spiel, but now you move on.

 

[G and J]

2 hours ago, saveasteading said:

My view us that sips gets specified by architects for schools etc, and isn't challenged so it's easy money. I've been confronted for 20 years by glossy mags telling me it's the only way. Some fall for it. You have not. For a while you were convinced by the spiel, but now you move on.

 

In truth I remained open minded, but to give a technology the best chance of being judged fairly one has to try hard to devise the best option.

 

3 hours ago, saveasteading said:

This should be routine. Change spec from plywood or osb, to cement board. Do you have a plan?

I started with the assumption that I’d be able to buy SIP panels with the outside made of cement board, but I failed to find a current supplier.  One did say they used to do them but they discontinued them due to problems (unspecified).  Our base case is exactly that, cement board sheathing our frame. It is a lot more expensive than OSB3 though. 

[joe90]

9 minutes ago, G and J said:

In truth I remained open minded, but to give a technology the best chance of being judged fairly one has to try hard to devise the best option.

Good for you, not everyone does this. If I were to build again (after years of reading about the many options on here ) i would stick frame with cellulose blown insulation. Personally I don’t like plastic type insulation (unless it’s the only option i.e under slab).

[saveasteading]

15 minutes ago, G and J said:

In truth I remained open minded

That is fair, or you would not have been asking on here.

 

16 minutes ago, G and J said:

discontinued them due to problems (unspecified).

that would be a lack of design expertise, absence of furnace tests and not having appropriate insurance.

 

19 minutes ago, G and J said:

cement board sheathing our frame. It is a lot more expensive than OSB3

Not stupidly so if you can shop around.  OR buy the cheapest one that has the fire resistance but may be too thin for structural use, and fix it on osb.

[saveasteading]

14 minutes ago, joe90 said:

the only option i.e under slab

I wonder why the mineral wool market has given up on this. There use to be Crown Floor Slab (Owens Corning) , with r= 0.031

I used it in an upper floor once, mainly for sound, with the floor boarding sitting directly on it.

 

And is there another economcal way to put a metal roof on a shed conversion?  150mm of Composite is a big lump to buy and to handle.

I will look at built-up with mineral wool.

Edited June 15 by saveasteading

[Iceverge]

How about a stick frame with OSB sheathing and a mineral wool layer before cladding?

 

Something like rockwool frontrock external to a stick build? Sorry fire regs aren't my strong point. 

 

For a thin high performance wall, thermal bridging really does have a big effect as you can't compensate by just making everything thicker.

 

A repeating 100mm stud will be much worse than a repeating  200mm stud for instance.

Edited June 15 by Iceverge

[saveasteading]

5 minutes ago, Iceverge said:

fire regs aren't my strong point. 

a good point. i haven't looked back at this project's details, but being under 1m from a boundary changes the rules. plasterboard will suffice inside, but the outside needs to be non-combustible. so cement board or masonry/ maybe brick slips.  If it is only spread of flame , then maybe some paints will do it.

[G and J]

I clearly need to research cement board prices more, I did my coatings on what I could quickly find in more than one place so as to reduce the risk of skewed results from a particular offer, so I readily accept I may have overestimated the stick build related costs.  The SIP ones were from quotes capable of acceptance, so I’m more confident in them (but not necessarily in how comprehensive my list of things needed in addition to those quotes….)

 

The target is a mostly two storey, mostly slate pitched roofed, mostly vertical larch clad, with some render, low risk house.   Low risk means nothing ground breaking or bleeding edge, I seek the best options for us amongst the tried and tested.  Sadly my curiosity demands I understand the less mainstream, but I bring myself back to heel soon enough.  I hope.

 

We soon start detailed design with the architects, and though I’ve a lot more on my knowledge shopping list, I’m already a much more informed decision maker.

[scottishjohn]

question?

 what is special about your build that requires cement fire proofing ?

[G and J]

1 minute ago, scottishjohn said:

question?

 what is special about your build that requires cement fire proofing ?

The outside walls of our house are within a metre of our boundary on both sides.  On the south side there is bang on a metre wall to wall with next door.  On the north side it’s a whopping 1.5m.  At the planning drawing stage the architect mentioned that we’d need to use fire resistant sheathing on the frame.  Apparently part built timber frames make rather intense bonfires.  😕
 

I’ve not researched this, as on a few quick searches it appears credible, so I've accepted it as a constraint.  
 

He also was ok with larch cladding, but I think that will need to be treated for fire resistance.