Timber framed VS SIP build.

[gustyturbine]

Hi all,

 

I recently managed to get planning permission in Aberaeron despite many NIMBY objections.

I have built once before with brick and block. It went well although with my GSHP and a family of 5 running costs are fairly hefty.

So, the next build!!

Initially I was thinking block inner and outer skin with partially filled cavity due to driving rain in these parts (100mm PIR board) inside cavity, partially clad externally with dark timber and smooth render the rest. Heating ASHP, 10kW PV with MVHR. 3g with no horrible trickle vents.

Now, I'm considering a SIP build to reduce energy costs. I suppose my concern living in a very exposed part of the world is that would driving rain manage to get through the membrane and wet the SIP's in time. would it make sense to still build a block or brick outer skin? If I did this then I can see costs escalating quite considerably. 

How do SIP houses compare against TF? I know that SIP's are much better from an airtightness point of view. I would hope that MVHR would stop mould building up. Thoughts and experiences welcome. Thanks all.

[Kelvin]

There’s no reason for water to penetrate the outer skin. You’d have much bigger problems if that happened. 
 

Can you clarify what you think you mean by timber frame? Do you mean stick built on-site? Also are you talking about a timber kit company supplying the SIP panels or having them made to an architect’s design. SIP panels aren’t necessarily more airtight by design than any other timber framed building, it’s all in the details. 
 

My house is a timber clad space framed timber kit from a kit company. We are atop

a hill and  get the weather for sure. I have no worries about wind driven rain though. I’d still have no worries if we were on the Atlantic coast. Plenty of timber clad kit buildings dotted around the Scottish Islands. 
 

If I was to ever do this again I’d go with MBC and blown cellulose if building a timber kit. Stick built on-site if not. I’d also look at ICF as that is inherently airtight but again it’s all in the details. 
 

 

[gustyturbine]

Hi Kelvin,

 

Many thanks for the comments.

The SIP's quote was from SIP suppliers following supply of my architects drawings.

Most TF houses around here are built panels off site although I'm sure some are stick built.

I'm off to Google MBC.

Thanks.

[Kelvin]

To clarify my comments. My reasoning for suggesting stick built if doing it again comes down to financial exposure going with a timber kit company. There are a few threads about it on here. Basically with a timber kit you have to front up the money before the kit arrives on site with very little to no financial protection should the kit supplier go bust. 

[IanR]

1 hour ago, gustyturbine said:

I know that SIP's are much better from an airtightness point of view. 

Don't believe what the SIPs companies tell you without fully researching.

SIPs are liked by volume builders, when combing with a masonry rain screen and only wishing to achieve Building Regs levels of performance.

If you are going timber frame, with a lightweight rain screen, on a one-off self-build there are better options than SIP with better U values, decrement delay and air tightness. 

[Kelvin]

Yes SIP would be my last choice. 

[saveasteading]

3 hours ago, IanR said:

SIPs are liked by volume builders

Volume builders don't supervise like we do, and choose the cheapest workers, so they need to idiot-proof the process.

 

Our stick-build was made into panels on site, so that is yet another option.

Zero risk on materials, but you need  a good joiner  / carpenter whichever name represents  the more skilled in your area.

It really depends how much management you plan to do, or if you prefer to (and can afford to ) use package deals. 

[JohnMo]

If you are actually doing the build, build with what ever method you want and are comfortable with. Any build method can get excellent results, as far as u value is concerned.  Not sure PIR in cavity would be my number one choice. You would be better with a wider cavity and blown insulation.

 

If you are not actually building, but paying someone else to it, choice a method the used in the local area, so builders are easy to get and you can get competition to quote.

 

Unless you are building circa 500m2 plus, there should be no reason why a good self build will need 10kW ASHP? Specifying the size before you actually know how you are building putting the cart before the horse.

[gustyturbine]

Hi all, many thanks for the valued comments and I am questioning the SIP idea.

TBH initially I was going block (again) as it's the common practice around here. Insulation board on the outer face of the inner skin. Building regs insist on the 50mm air gap within the cavity so generally the cavity has 100mm PIR board. Most local trades are either blockers or chippy's building factory built TF. If I went block I was going to use block and beam floors for sound insulation (3 kids). 

However, factory built TF or stick built seems to get a lot of positive feedback on here. My current house used Pozi/wolf joists and the sound transfer is disappointing and I hear kids talking upstairs. 

I'm guessing that TF factory built allows for a faster build but on site could work out cheaper. My only concern with factory built TF is issues with water leaks etc in bathrooms can cause problems. Block and beam would be more tolerant. Hanging heavy object with block walls is easy. TF means you need to be more careful and plan ahead?

I'm also concerned though that lowering energy demand for a modern build is essential imo.

My PV at 10kW wasn't saying that I needed a 10kW ASHP as I also have an EV. I just want to be generating as best I can rather than importing at current prices. Thanks all.

[JohnMo]

Read up on passivhaus builds with block work, see how they do it.

 

Also many on here have used blocks with wide cavity and say to steer clear of PIR; good in theory but in practice not easy to install with good results.

[joe90]

Just now, JohnMo said:

Also many on here have used blocks with wide cavity and say to steer clear of PIR

I am one of those, block inner, 200mm cavity full filled with dritherm and brick outer skin 👍, the only PIR is under the slab, it’s the only insulation that will carry a slab.

[gustyturbine]

1 hour ago, joe90 said:

I am one of those, block inner, 200mm cavity full filled with dritherm and brick outer skin 👍, the only PIR is under the slab, it’s the only insulation that will carry a slab.

The trouble is that our Building Control will not allow a cavity to be full filled with insulation. We must have an air gap. 😞

[joe90]

21 minutes ago, gustyturbine said:

The trouble is that our Building Control will not allow a cavity to be full filled with insulation. We must have an air gap. 😞

Well I had that conversation with our BCO and  when I showed him the bba certificate for full fill he changed his mind. Another example of no common policy throughout the country on these matters 🤷‍♂️

[JohnMo]

It may be the difference between a breathable insulation and not breathable (PIR in this category)

[ADLIan]

36 minutes ago, joe90 said:

Well I had that conversation with our BCO and  when I showed him the bba certificate for full fill he changed his mind. Another example of no common policy throughout the country on these matters 🤷‍♂️

compliance with a BBA cert is an alternative way of complying with the Regs rather than using Approved Docs. Most built in cavity insulation will be approved for severe or very severe exposure zones but look at the small print for the need for render or have flush/weather struck mortar pointing. 
 

Has nothing to do with insulation being breathable or not.

 

Above applies to masonry. Sips, timber frame or metal frame must have 50mm clear cavity between insulation and brick/block outer.

Edited August 11, 2023 by ADLIan
Technical

[JohnMo]

2 hours ago, ADLIan said:

Above applies to masonry. Sips, timber frame or metal frame must have 50mm clear cavity between insulation and brick/block outer.

What happens when you fill the cavity (block and brick) with poly beads, as those would not comply?

[ADLIan]

Depends upon what’s in their BBA Cert. May be limited to max ‘severe’ exposure zone with masonry inner and outer. 50mm cavity still applies with sip and framed construction.

Edited August 11, 2023 by ADLIan
Clarify

[Nickfromwales]

On 10/08/2023 at 16:13, gustyturbine said:

Hi Kelvin,

 

Many thanks for the comments.

The SIP's quote was from SIP suppliers following supply of my architects drawings.

Most TF houses around here are built panels off site although I'm sure some are stick built.

I'm off to Google MBC.

Thanks.

You may also do well in asking Adam Wilkinson (Wilkinson Passive House) for a quote. One of the rare few who are meticulous but not 'champagne money' to be so.

I am also a huge fan of MBC btw. They are QUICK!

Both offer turnkey solutions (foundation > frame > insulation > guaranteed airtightness score) which means they have to produce the minerals  

SIPS fails to impress me tbh. Would be my last choice also.

[Nickfromwales]

Avoid a SIPS roof. Noisy as feck.

[LA3222]

I have a SIP build, I am not sure why folks who don't have one are dismissive. The one thing I have learned through doing a self build is probably the single most important thing to take into consideration....the method of build is irrelevant, you'd be splitting hairs and if you standardise the ask I.e insulation/airtightness then king becomes cost; it is the application of the chosen method which is key. A supposedly great system can be Total shite if cobbled together by a bloke with one eye and three digits missing off each hand.p

 

You can achieve really tight specs with whatever method, it's the effort in monitoring that is essential.

[saveasteading]

39 minutes ago, LA3222 said:

I am not sure why folks who don't have one are dismissive

Not dismissive. Cost and lack of adaptability are the two main reasons I've never used it. and large prepayments.

[Nickfromwales]

6 hours ago, LA3222 said:

I have a SIP build, I am not sure why folks who don't have one are dismissive.

I just find them acoustically transparent tbh. SIP's roof is the last choice for me, with the latest architect being dismissive by saying "the interior will be connected to the outdoors" which actually meant when it rains had you'll need to turn the TV up. I pointed this out to the client before the ceilings got closed off, and they agreed to spend some more money adding 100mm of acoustic insulation to control the issue, as best as could be achieved, retrospectively.

A cellulose blown frame and roof, al-la MBC / WPH is graveyard quiet by comparison. These are genuinely miles apart in performance. That's not guesswork btw, that's from being stood inside them and being able to tell the difference.

[MikeSharp01]

7 hours ago, LA3222 said:

 

You can achieve really tight specs with whatever method, it's the effort in monitoring that is essential.

Absolutely - anything from stick / brick to factory prefab can be done well, or indeed poorly, and all of the methods have their pros & cons. Stick/brick is time consuming and somewhat skilled but you get to make choices as you go along while factory prefab means making all the decisions up front and so is far less evolutionary (should you wish to evolve your build - we didn't, we wanted to follow the architects ideas as closely as we could.)  Then its down to the range of technologies chosen and how they work together to create the home (house).

[Kelvin]

Part of the reason we chose the space frame system over SIP (as the kit company offered both) was for the aesthetic of the wider walls creating deeper reveals at the windows. 

[Thorfun]

19 hours ago, gustyturbine said:

My current house used Pozi/wolf joists and the sound transfer is disappointing and I hear kids talking upstairs. 

did any Rockwool get installed between floors? interested to know as we've put 100mm of Rockwool between our posi-joists and I'm hoping that will sufficiently reduce the noise transfer.

 

19 hours ago, joe90 said:

the only PIR is under the slab, it’s the only insulation that will carry a slab.

EPS of a structural engineered calculated compression rating will