SIP build- how to finish externally behind larch cladding?

[mattp22]

Hi, I'm building a house in Scotland using SIP construction for insulation quality, airtightness and speed of build. Plan is to clad in larch externally like image below. But speaking to several mortgage companies who will take on the long term mortgage (after self-build mortgage finishes in 9 months) it seems most are very wary of SIP construction with only timber cladding. A couple of highstreet lenders have said it's a 'possibility' (halifax and santanter) but most want masonry external skin. If i go to non-highstreet lender who are more understanding of purely timber SIP build the interest rate seems to be more like 4% rather than 2% so it makes a major difference to mortgage payments. 

 

I've therefore decided (just to satisfy mortgage lender) to add a middle skin of lightweight concrete block between SIP frame and larch cladding. My question is do you think the concrete block can be left painted black behind the larch, or will i need a more substantial finish on the concrete block because the larch installation has such large gaps (15/20mm spacing). I don't want to have issues with moisture travelling through the masonry and condensing on the SIP or at soleplate. Very frustrating to have to add the totally unnecessary masonry but over 5 years i calculate mortgage saving will be around £10k and i think block cost will be around £5k. Thanks.

 

 

[Carrerahill]

You are going to end up with a substantial house here, so although you are appealing to bankers who don't really get this building with SIPs deal you are also getting to my mind the best of both worlds.

 

So what is your planned make-up? Sip panel wrapped in a membrane then a cavity then block skin? 

 

In terms of how you end up cladding the block I would be thinking of the following:

Whatever I cover the block in will not be easily repaired or replaced - full cladding off job, so it needs to last.

If I paint it, it may flake and bubble in 5-10 years, where does that leave me?

If I fix treated battens or possibly galvanised metal etc. to the block with good quality fixings then membrane over that, as long as I use one of these exposed membranes that you often see behind cladding like this then the inner structure is going to be protected and the "consumable" aspect is just the larch and membrane (it will need to be designed for full life exposure, i.e. UV stable) which can be changed out every 30-50 years.

I would also be thinking about alternatives, possibly longer lives alternatives. 

I would also consider having the membrane in direct contact with the block, then stained black battens over the top (like a roof make-up) as this would also mean the membrane didn't get as much moisture coming into contact with it, which could then sit directly behind the cladding and would let the cladding dry out quicker. 

 

I have seen this done so many ways from log cabins we have stayed in to modern architectural wonders in the city centre with cladding and I am always that guy poking about looking to see how it was done and have so far never seen "the way" as there seems to be many.

 

Use black bricks!

[Temp]

The problem is that there is nobody certifying or approving non traditional construction  techniques for life expectancy. The government should consider setting up a body (if the NHBC won't) to do this job. Its going to be important if we are ever to mass produce houses in factories in the UK.

 

 

[Temp]

https://www.proctorgroup.com/how-to-choose-the-right-membrane-for-open-jointed-cladding

 

[LA3222]

29 minutes ago, Temp said:

The problem is that there is nobody certifying or approving non traditional construction  techniques for life expectancy. 

What do you mean by certifying? I had no trouble getting a warranty from Protek for my build, likewise I had no issue getting a self build mortgage for it.

 

I have yet to seek a remortgage with a high street bank but maybe I'll hit some walls there?‍♂️

 

I have SIP with block outer skin - from what I've read (briefly!) leads me to believe its the amount of timber in a build which adversely affects lenders perceptions I.e. a TF clad in timber not good, TF with masonry outer skin much better perceived?

 

Anyway, off topic slightly - @mattp22 I cant advise on the membrane but I think you've made the right choice to use block outer skin. I have wrapped my SIP build in rendered block. I do have a side abutment which I intend to clad with cedral click onto the blockwork buts it more straightforward than ypur job as i won't have shadow gaps to contend with. As suggested, battening and then wrapping sounds like the best way forward.

[mattp22]

46 minutes ago, Carrerahill said:

You are going to end up with a substantial house here, so although you are appealing to bankers who don't really get this building with SIPs deal you are also getting to my mind the best of both worlds.

 

So what is your planned make-up? Sip panel wrapped in a membrane then a cavity then block skin? 

 

In terms of how you end up cladding the block I would be thinking of the following:

Whatever I cover the block in will not be easily repaired or replaced - full cladding off job, so it needs to last.

If I paint it, it may flake and bubble in 5-10 years, where does that leave me?

If I fix treated battens or possibly galvanised metal etc. to the block with good quality fixings then membrane over that, as long as I use one of these exposed membranes that you often see behind cladding like this then the inner structure is going to be protected and the "consumable" aspect is just the larch and membrane (it will need to be designed for full life exposure, i.e. UV stable) which can be changed out every 30-50 years.

I would also be thinking about alternatives, possibly longer lives alternatives. 

I would also consider having the membrane in direct contact with the block, then stained black battens over the top (like a roof make-up) as this would also mean the membrane didn't get as much moisture coming into contact with it, which could then sit directly behind the cladding and would let the cladding dry out quicker. 

 

I have seen this done so many ways from log cabins we have stayed in to modern architectural wonders in the city centre with cladding and I am always that guy poking about looking to see how it was done and have so far never seen "the way" as there seems to be many.

 

Use black bricks!

 

Thanks for your comments. Construction will be 160mm SIP kit, membrane, 50mm cavity, 100mm lightweight block, something black, 18mm batons then 22mm horizontal larch . That link to Proctor Group is great- i've been looking for weeks and hadn't found anything but that product sounds good.

 

Paint flaking was a concern for me too. Ideally larch will be nailed on to batons so yes would be impratical to remove every 5-10 years to paint the blockwork. I had considered corrugated black steel on to blockwork then batons then larch, but i think the mortgage lender will get spooked with use of larch + steel sheet. I could use the Proctor membrane on top of corrugated panel to conceal it i suppose and lender will be none the wiser.

 

Proctor membrane straight on to masonry sounds like the way to go, using black batons to secure membrane down, but Proctor data sheet says 5000 hours UV tested which is only 208 days direct sun. Obviously UV resistance not applicable at night time, and the gaps between larch only 18mm so gap for UV to penetrate is small and position of sun will make angle of 'attack' tight, but still doesnt sound like the Proctor product will be much better than 5-10 years expectancy like paint option. I'll email them to ask rather than blethering here!

 

black bricks are nice- but too expensive unfortunately to then be covered by larch

 

 

[mattp22]

9 minutes ago, LA3222 said:

What do you mean by certifying? I had no trouble getting a warranty from Protek for my build, likewise I had no issue getting a self build mortgage for it.

 

I have yet to seek a remortgage with a high street bank but maybe I'll hit some walls there?‍♂️

 

I have SIP with block outer skin - from what I've read (briefly!) leads me to believe its the amount of timber in a build which adversely affects lenders perceptions I.e. a TF clad in timber not good, TF with masonry outer skin much better perceived?

 

Anyway, off topic slightly - @mattp22 I cant advise on the membrane but I think you've made the right choice to use block outer skin. I have wrapped my SIP build in rendered block. I do have a side abutment which I intend to clad with cedral click onto the blockwork buts it more straightforward than ypur job as i won't have shadow gaps to contend with. As suggested, battening and then wrapping sounds like the best way forward.

 

i think with rendered block outer skin you should be fine with highstreet lender and thus lower % rate. My mortgage broker has spoken to about 20 lenders and it seems with masonry element then about half are happy with SIP construction. Timber cladding on masonry reduces pool further though but that's the look we want (and Planners!)

 

Last time i spoke to Protek they wanted £5k for my warranty but that was without masonry element, timber only construction. Hopefully they'll reduce it a bit now.

 

Was your SIP kit BBA approved if you don't mind me asking? I am probably using a company in Fife for kit but they are not BBA approved (yet) and i'm a bit wary of consequences.

 

[mattp22]

36 minutes ago, Temp said:

https://www.proctorgroup.com/how-to-choose-the-right-membrane-for-open-jointed-cladding

 

 

thanks for link, that sounds ideal

[Thorfun]

our architect recommended this https://www.dupont.co.uk/products/tyvek-uv-facade.html as a breathable membrane below our shadow gap cladding. it doesn't have any logo or markings and comes with a 10yr warranty. might be worth a look?

 

I've asked our TF company to use this instead of the shiny silver membrane as we don't want silver showing through our charred larch cladding shadow gap! I looked at the Protect version but that has 'Protect' in red on the outside and also states the 5000hrs only with no warranty. I think that the 5000hrs refers to the BS standard for accelerated testing of the membrane though. but don't quote me on that. so it's not to say that it won't last more than 5000hrs but has only been tested to 5000hrs. if that makes sense? I'm sure someone more knowledgable than me on all of this will be along soon to refute or confirm what I've said. ?

 

[mattp22]

5 minutes ago, Thorfun said:

charred larch cladding

 

very nice- that's what we wanted but Planners not up for it. Where did you get it from if you don't mind me asking?

I'll check out Dupont- thanks

 

[Thorfun]

1 minute ago, mattp22 said:

 

very nice- that's what we wanted but Planners not up for it. Where did you get it from if you don't mind me asking?

I'll check out Dupont- thanks

 

not ordered it yet, not even broken ground yet! but we got a good quote from https://shousugiban.co.uk and the samples looked really good. but, nearer the time of ordering I will get further quotes from other companies. 

 

we're having a combination of the charred larch and normal larch to get the brown/black contrast in places. hopefully it should look lovely. ?

[LA3222]

16 minutes ago, mattp22 said:

Was your SIP kit BBA approved if you don't mind me asking? I am probably using a company in Fife for kit but they are not BBA approved (yet) and i'm a bit wary of consequences.

 

Yes. My frame is Kingspan Tek, supplied by one of their delivery partners.

 

Not sure if I would go with a non BBA approved one, nor sure what that would affect later on down the line.  I'm sure it is to the same standards as the one I used, but iirc I had to supply BBA paperwork to building control for it - not sure what would have been said if it wasn't BBA approved.  You're north of the border so it may be different up there.

[Mr Punter]

The Dupont Tyvek UV Facade membrane is excellent.  A matt black finish.

[the_r_sole]

That's adding a big cost onto a build there, worth pricing out the new build up and seeing how long the "payback" is?

What broker are you using? And have you spoken to any other brokers? 

[Mr Punter]

I have seen an increasing number of lenders who want a brick or blockwork skin.

[Mr Punter]

Would cement based cladding be of interest?

[mattp22]

44 minutes ago, the_r_sole said:

That's adding a big cost onto a build there, worth pricing out the new build up and seeing how long the "payback" is?

What broker are you using? And have you spoken to any other brokers? 

 

not sure i've got an option unfortunately if comments from lenders are to believed. i've not costed for the blockwork accurately yet but have estimated £6k inc. labour for 160 sq mtrs (based on several online calculators). In terms of mortgage savings- around 2% rate from highstreet lender should be possible given location, non-trad construction and loan to value. Specialist lender who would accept SIP + cladding with no masonry would be 3% if lucky but closer to 4% in reality, and construction type would deter re-sale if i ever had to move. Over 5 years that would cost me an extra £8k @ 3% or £16k @ 4% in repayments so makes sense to go for blockwork now even if it is hugely frustrating and unnecessary. 

Broker i've used for several mortgages and she has really done a lot of leg work on this construction method for me.

[mattp22]

50 minutes ago, Mr Punter said:

Would cement based cladding be of interest?

 

thanks, and it is something we looked at, but not quite the style we're after. PP is for larch cladding too.

[Mr Punter]

How deep is the SIP?  Does it need any extra insulation?  I am just trying to work out the overall wall thickness.  I would rather be in your place during a severe storm than with rainscreen cladding supported by SIP panels.

[mattp22]

2 minutes ago, Mr Punter said:

How deep is the SIP?  Does it need any extra insulation?  I am just trying to work out the overall wall thickness.  I would rather be in your place during a severe storm than with rainscreen cladding supported by SIP panels.

 

SIP is 169mm, 0.2 w/M2. I understand with blockwork and cavity this will drop to around 0.16 w/M2. We were going to increase panel thickness/ insulation anyway which added £2k to SIP cost, but no need now that we're adding blockwork- so the £2k can be taken off blockwork cost i guess.

 

good point about protection in a storm, it's not like we're 10 metres from the Atlantic, oh.. no.. wait minute...

[SuperJohnG]

11 hours ago, mattp22 said:

Last time i spoke to Protek they wanted £5k for my warranty but that was without masonry element, timber only construction. Hopefully they'll reduce it a bit now.

 

Was your SIP kit BBA approved if you don't mind me asking? I am probably using a company in Fife for kit but they are not BBA approved (yet) and i'm a bit wary of consequences.

 

 @mattp22

I am using a company in Fife for my SIPS kit (just about to place order in next 2 weeks. I'm using SIPS eco, worth dropping me a message of who you are using and I can give you the low down on all SIPS suppliers in that area, one in particular should be avoided in my opinion. 

 

SIPSECO let their BBA cert expire in 2014, however they are CATG approved, but are currently renewing their BBA cert and this is a condition of my purchase with them.

 

I have a quote from Protek for £3k for my structural warranty. 

 

I had the same struggles as you with the build up and followed @LA3222 's build so far in detail. I am doing an insulated passive slab, and its 2-3k extra for the ring beam for the outerblock work skin and hence I have moved away from it for that reason, but also because I felt I didn't want to rely on that wet trade and couldn't really quantify the costs. I seen no major benefit, hence I have opted for renderboard (Knauff aqaupanel) finished in a thin coat render system. 

 

Over 75% of my house is finished in render on board with the main annex for the open plan area on exactly the same as you - rainscreen cladding. I'm doing the normal build up of SIPS, Protect UV 5000 facade, then treated batens (painted black or whatever - haven't figured out that part) then Siberian larch cladding with hidden fixings in the RW014 profile from Russswood. 

 

Ecology had no issue with my build up, however I did some investigation into high street lenders (but not much) as it was slightly concerning but seemed ok...I've yet to do any real research. on that part.  

 

FYI - I'm in East Ayrshire, on the west coast, it rains A LOT! Albeit I am not at the coast. I do have a very large canopy though over my larch cladding so somewhat more protected possibly. 

 

9 hours ago, Mr Punter said:

I have seen an increasing number of lenders who want a brick or blockwork skin.

 

@Mr Punter it would be good to hear more detail on this? 

 

 

Picture added to help 

Edited August 27, 2020 by SuperJohnG
Picture added,

[Mr Punter]

1 hour ago, SuperJohnG said:

@Mr Punter it would be good to hear more detail on this? 

 

About 4 months ago I read a long document that had criteria from many lenders.  I can't remember if it was aimed at valuers or brokers, but with timber frame lots wanted brick / block outer leaf.  It was not the main thing I was looking at.  Flood risk, above commercial, multi storey, tenant type were more of interest.  Grenfell has put everyone off non brick or block.  I think Trada etc did no favours by not emphasising fire risk.  Once you cannot easily gain insurance, you cannot get funding and your asset is worth sod all.

[mattp22]

11 hours ago, SuperJohnG said:

I am using a company in Fife for my SIPS kit (just about to place order in next 2 weeks. I'm using SIPS eco, worth dropping me a message of who you are using and I can give you the low down on all SIPS suppliers in that area, one in particular should be avoided in my opinion. 

 

SIPSECO let their BBA cert expire in 2014, however they are CATG approved, but are currently renewing their BBA cert and this is a condition of my purchase with them.

 

I have a quote from Protek for £3k for my structural warranty. 

 

I had the same struggles as you with the build up and followed @LA3222 's build so far in detail. I am doing an insulated passive slab, and its 2-3k extra for the ring beam for the outerblock work skin and hence I have moved away from it for that reason, but also because I felt I didn't want to rely on that wet trade and couldn't really quantify the costs. I seen no major benefit, hence I have opted for renderboard (Knauff aqaupanel) finished in a thin coat render system. 

 

I'll check out Ecology again but i couldnt find any standard % rates on their site, presumably because they don't deal with standard builds, but any more than 0.75% points more on mortgage would push the numbers in masonry's favour for me. Bonkers in 2020, but that's mortgage lenders for you.

For what its worth i've been advised renderboard over the SIPs would satisfy many high street lenders and therefore get you the lower interest rates.

 

SIPECO is the way I am going too, with Isoquick slab (i think). Isoquick were £6-8k depending upon insulation level but that's for SIP/timber only build. I hadnt realised adding masonry would bump the cost up so much  so i might revisit Kore and ask my ground works crew to install to lower costs (although they have not done an insulated slab before, so that should be fun!) Good to know that ECOSIPS are getting their BBA cert so soon- they just told me it was in progress. 

 

That's cool you're pulling the trigger in 2 weeks, when are you hoping to start founds and SIPs? Are ECOSIPS doing SIP install too?

 

[SuperJohnG]

3 hours ago, mattp22 said:

 

I'll check out Ecology again but i couldnt find any standard % rates on their site, presumably because they don't deal with standard builds, but any more than 0.75% points more on mortgage would push the numbers in masonry's favour for me. Bonkers in 2020, but that's mortgage lenders for you.

For what its worth i've been advised renderboard over the SIPs would satisfy many high street lenders and therefore get you the lower interest rates.

 

SIPECO is the way I am going too, with Isoquick slab (i think). Isoquick were £6-8k depending upon insulation level but that's for SIP/timber only build. I hadnt realised adding masonry would bump the cost up so much  so i might revisit Kore and ask my ground works crew to install to lower costs (although they have not done an insulated slab before, so that should be fun!) Good to know that ECOSIPS are getting their BBA cert so soon- they just told me it was in progress. 

 

That's cool you're pulling the trigger in 2 weeks, when are you hoping to start founds and SIPs? Are ECOSIPS doing SIP install too?

 

Hi Matt, 

 

Standard current rate for the Ecology self build mortgage is : 4.15%, once you complete this drops in line with your final EPC rating (they call it C-change discount). Up to  a maximum of 0.75% reduction. However you would want off that rate after the 2 year period is up to get high street rates (as you are trying to do).

Thanks for the renderboard info with high street lenders, that's helpful! 

 

Careful not to get confused between SIPS ECO and Ecosips - they are different companies. 

 

I found Isoquick to be significantly more expensive than Kore. 

 

Hoping to get founds done in 8-10 weeks , then maybe kit up before xmas, but just going with the flow at the moment as only just in with building warrant. 

 

SIPS ECO (or more specifically their contractor teams) will be doing install yes. 

[mattp22]

1 hour ago, SuperJohnG said:

Careful not to get confused between SIPS ECO and Ecosips - they are different companies. 

 

lol, i hadnt realised- i am speaking with SipsEco just now. Sorry for typo.

 

Seems EcoSips are based 20 minutes away from them- confusing! Must be a story there...

 

I've got Kore at about 60% of Isoquick cost but excluding installation. I will be remote managing so thought supply & fit might be less of a headache.