First timers attempting an ICF and Oak Frame house in Devon

[Russell griffiths]

21 minutes ago, MCoops said:

Wow, 30mm - that is something we definitely can't encounter as we have to spec the Oak frame to be xmm off the ICF wall - we were thinking to allow just a small gap, maybe 20mm, to allow a wet plaster skim behind, but will definitely look into this more and allow more wiggle room. 

I would think you will need to plasterboard behind the oak frame, not wet plaster. 
 

there is a lovely oak frame cafe near me that has plastered walls behind the oak posts, the areas the plasterer couldn’t get his trowel into look rough as a badger’s backside, the gap was not big enough for him. 
 

I would slide a full board behind each post and then leave 40mm min so he can get his skim coat behind the post. 
 

you will need to wrap the posts up as plaster in the oak grain is a pig to get out. 
 

im thinking oak trusses sitting on top of the icf walls, with false oak posts would be far simpler. 

Edited February 4 by Russell griffiths

[Mr Punter]

Someone on here did an oak frame with oak visible inside and out.  I can't find the person, but here is the house:

 

https://www.rightmove.co.uk/house-prices/details/england-65891074-69232953?s=09f1fd364ad88af843b86a954972dc9081ac27208edb81c15a43198f3100ab4f&v=media&id=media0&ref=photoCollage

[Nickfromwales]

2 hours ago, MCoops said:

Wow, 30mm - that is something we definitely can't encounter as we have to spec the Oak frame to be xmm off the ICF wall - we were thinking to allow just a small gap, maybe 20mm, to allow a wet plaster skim behind, but will definitely look into this more and allow more wiggle room. 

Yes, was a shock for that client, but even with very meticulous builders on site that was the max undulation that they had to overcome.

 

There are different experiences from different members, please all remember that these are simply my experiences and folk can do as they wish with the info, but I am an advocate of people knowing there's a hole in the ground ahead of them, vs offering them a ladder to get out after they've fallen in said hole.....better to know the pitfalls in advance of making a choice, and then you have the ability to make your own, informed, decision.

 

@MCoops are you decided on a type yet? Just I can adjust the info to be more focussed on the preference vs generalise etc, to get you over the line a bit quicker. Are these to be dwarf walls, or full elevations with a full oak frame within?

[Nickfromwales]

2 hours ago, MCoops said:

Though, everyone I've spoken to has had a blow out on their woodcrete pours

And on EPS, anyone who says they haven't had at least a minor blowout was either very lucky, lying, or braced it all enough to make a bamboo scaffolder happy 

[Alan Ambrose]

>>> Plan is to get the Oak frame in place first. This is all being made off site so will just be craned in and fixed. Then the ICF walls will be built around the outside. Then the SIP roof panels will be added. 

 

Sounds a good plan. FYI am I trying to get an understanding right now of how accurate, straight and upright you can expect oak frames will be once erected.

 

>>> We need to get the Oak out of the elements as quickly as we possible as the rain affects the finish, and obviously the drying out time increases the wetter it gets. 

 

It shouldn't absorb much water, but the more stained it gets, the more work it is to get it unstained.

 

>>> you will need to clean the oak with oxalic acid when it’s all done to bring back the natural colour. 

 

Or lightly sand/bead blast it or a combination of both - acid on the very stained bits, then blast all over.

 

>>> we were thinking to allow just a small gap, maybe 20mm, to allow a wet plaster skim behind, but will definitely look into this more and allow more wiggle room. 

 

The conventional way is to allow 15+mm (more if you can't guarantee how wobbly the icf is) and tuck the plasterboard behind the posts. Something like this, which has a 20mm gap also (defined by the spruce strips):

 

  

 

[MCoops]

20 hours ago, Russell griffiths said:

...im thinking oak trusses sitting on top of the icf walls, with false oak posts would be far simpler...

Easier indeed, but what's life without a challenge hey 🙃

 

The Oak will be fixed to the ICF behind each post, so we can't slide a board in fully behind it. What the Oak company have done in their show home looks good though, they've skimmed behind. I think we will just need to leave more of a gap for trowel access. 

 

We've had a few plaster incidents with Oak floor, so I know the pain of cleaning that up! One I will 100% avoid in this build! 

[MCoops]

17 hours ago, Nickfromwales said:

@MCoops are you decided on a type yet? Just I can adjust the info to be more focussed on the preference vs generalise etc, to get you over the line a bit quicker. Are these to be dwarf walls, or full elevations with a full oak frame within?

@Nickfromwales ICF is the full elevation, up to eaves, including gable ends, of which we have 3 as the house is an L shape. Full Oak frame within. 

 

We do need some help erecting the ICF (2 jobs, child in school, not living that close to site at the moment, we can't build it all) - which is also having an impact, as we are really struggling to find anyone that will work with woodcrete blocks. People only seem to want to work with the EPS blocks, all had bad experiences when building with woodcrete on jobs. We have had quotes from Nudura for supply which we are happy with, and Ecobrix. 

[Nickfromwales]

1 hour ago, MCoops said:

People only seem to want to work with the EPS blocks, all had bad experiences when building with woodcrete on jobs.

It’s mostly from additional costs for labour etc which clients just don’t see / aren’t aware of with woodcrete ICF. This massively affects their top lines and forces most to quote themselves out; it’s hard to find anyone decent enough to demonstrate this uplift before signing up vs the shitheads who get you signed into a contract full of exclusions / omissions and Carte Blanche mechanisms for adding ‘extras’ aka variation costs.

 

This can be massive on anything other than a simple ‘cube’, and after seeing one clients build cost go up by nearly 60% I said to myself “f*** that for a game of marbles”. 
 

EPS for me or TF, other than that I just don’t bother quoting for the job. Life’s already hard enough tbh, why make it harder? 
 

Great for DIY’ers with the time to write off, but commercially it is a ballache. 

[SteamyTea]

19 hours ago, Mr Punter said:

here is the house

Is that how to cover up damp.

 

[Iceverge]

On 04/02/2025 at 16:53, Mr Punter said:

Someone on here did an oak frame with oak visible inside and out.  I can't find the person, but here is the house:

 

https://www.rightmove.co.uk/house-prices/details/england-65891074-69232953?s=09f1fd364ad88af843b86a954972dc9081ac27208edb81c15a43198f3100ab4f&v=media&id=media0&ref=photoCollage

 

I know of a house like that. 

 

They even passed the airtighess test. 

 

Apparently all the gaps in the walls were just big enough to slip some £50 notes into the testers pocket.....

[Iceverge]

There's something in my head that still can't warm to the idea of ICF and oak frame. 

 

Perhaps it's the six times differing thermal expansion coefficients of oak and concrete.

 

Maybe it's the idea of minding the oak frame from the sloppy work of filling the ICF with concrete or bracing the inside of it during construction. 

 

Trying to get a clean finish on the internal walls in the joint between the oak frame and the flat plasterboard seems hard too. 

 

You could leave a gap but how exactly would you deal with this between floors for fire and sound transmission etc. 

 

I'm still sure there's a solution in my head somewhere, if only it would come out.....

 

Edited February 7 by Iceverge

[JohnMo]

Think I would be looking at a thermally broken stud wall and cellulose fill.  

 

If the oak is structural it would be a cheap structure to do.

 

[GaryChaplin]

On 30/01/2025 at 18:26, Mr Punter said:

What a great plot!

 

I understand the attraction of oak.  It is a traditional natural material.  Sadly for a house structure it does not work well as it is hard to achieve decent insulation and airtightness.  There are loads of other options, so keep an open mind.

 

You could always have an oak framed workshop / garage if you have the space.

It's not hard to insulate at all. Just create an continous insulation envelope on the outside. My self-build has walls under 0.12 W/m²K. 

[Alan Ambrose]

>>> Perhaps it's the six times differing thermal expansion coefficients of oak and concrete.

 

There’s a fairly time tested solution to this - the frame is more or less free standing inside or lightly connected to the external envelope. Check out any self build magazine and you’ll see an oak frame inside a brick external wall with various kinds of insulation between.

[Gus Potter]

On 30/01/2025 at 12:25, MCoops said:

We've got a structural green oak frame supporting the upper floor and roof, all visible internally. Then we're building the walls with ICF on the outside. We toyed with sips but weren't fans. We are sip paneling the roof though. 

I'm trying to get my head around how this is an economic build. Yes go for the wow factor.. I love oak frames. They live, breath and move about, but ICF walls are stiff for example. Then you need to sit them on some kind of foundation, could be a raft and all the time you add unwanted weight.

 

For me a small oak frame building should almost "float" on the ground and move with the ground and it's nuances. But if you take this design approach and then go putting in sensitive finishes such as large format tiles on the floor then you need to either spend more money in the ground or re detail your finishes. There is often no free lunch. But with a bit of eccletic thinking you can often have your cake and eat it.. if you put in the work to understand the building, the ground and put in plenty movement joints.

 

Incedentally when designing raft foundations we might choose to make them very stiff with lots of rebar.. say if there is a mining risk. Here we want the raft foundation to "stay together" so the whole house tilts a bit without breaking it's back.

 

But we also may design them to be quite flexible as the ground may settle differentially (a different depth of good load bearing clay from one end of the building to the other|)  In some ways an an oak frame is suitable for a flexible raft (often cheeper) as we just take the view.. everything is moving about so let's live with that. So long as it does not fall down then it can be ok to have a house that cracks a bit and lives! Maybe that is an eco friendly approach to design?

 

On 03/02/2025 at 15:08, MCoops said:

Luckily we have found some great SEs, but are doing all the design ourselves, so learning A LOT!

Well a plus + for that getting an SE in early.

 

Good designs are about taking a view on things, exploring options, ruling out others, review, develop and review again. You have done the right thing gettting an SE on board early. This will allow you to look at the design holistically from the load bearing ground up. There are great savings to be made by adopting this approach. Mnay Build Hubbers don't do this.

 

On 03/02/2025 at 15:09, Alan Ambrose said:

 

FYI - I'm having sensible conversations with them re frame supply only. You can get a rough number for retail oak in £ / m^3 from online suppliers. (Last time I calculated it was £2.3K/m^3.) Then see how much the joint work and erection adds to the quoted price and check whether it's honest. I figure the oak frame guys should be charging about 3x the retail cost / m^2.

Edited February 3 by Alan Ambrose

Cracking observation. That is giving me food for thought! 

 

Why.. because @saveasteading has tackled a really complex roof on a steading conversion. They got a competant local joiner to template the really difficult joints, some of the hip angles and joints were hugely challenging and then they executed the work effectively. Ok that was done in soft wood but you could easily do the same in green oak. The connection design is similar.. dowels or bolts. Oak is stronger than soft wood thus the connections (which often govern the design) are easier to make work.

 

My gut feeling is that a local joiner may not have the heavy tools / fabrication facility to cut complex rebates say in green oak.. but for a simple oak frame it think it may be doable on site.. after all a simple oak frame is just like a traditional cut / purlin type roof.. with 1/3 checks in the timber for the ceiling ties, half checks at the ridge and so on.

 

Edited March 4 by Gus Potter

[SteamyTea]

12 hours ago, Gus Potter said:

and put in plenty movement joints.

I would like to see the detail options for these joints.

When we used to manufacture large, bespoke GRP structures i.e. mosque domes, hospital walkway, external cladding (hard to believe that the fire regs were so loose in the 70s and 80s) I can never remember an SE being involved, even after I raised concerns about thermal expansion/contraction, let alone settlement.

The only times I can remember proper engineers being involved was with aviation railway work, but they took a safety first attitude.

We did a cabin mockup for Airbus that was used for training, even that was rigourously designed and tested, especially for fire and smoke.

[Gus Potter]

On 05/03/2025 at 11:29, SteamyTea said:

I would like to see the detail options for these joints.

It's a fascinating subject. For all on BH there are some general recommendations in the design codes, say for movement joints in brickwork / concrete blocks but mostly it's left up to engineering judgement and that is based on looking at the whole design holistically. Movement in buildings is one of the dark arts.. it's taken me 40 years to grasp the basics and I still learn from day to day.

 

A green oak frame is just a hard wood timber structure and we have a good idea about how this will move about and how to detail the other bits of the building that are connected to it and allow for the diffferential movement between the materials. All houses move about, bend in the wind and settle for example.

 

Take a passive / semi passive raft foundation. It sits on a thick layer of insulation which is a bit "squashy" and here we that into account. When designing I look at the materials, what needs to be supported, say walls and glass and how they behave and interact, then say OK.. how can I force the movement (which I know is going to happen)  to a place where I can control it better and how do I design the movement joints to cope with this particular structure.

 

A simple example may be where you know you have tiled floors transitioning to say engineered wood floors. The common sense thing here is to force the design so the movement takes place under the door threshhold where it can be hidden and not crack the tiles.

 

 

On 05/03/2025 at 11:29, SteamyTea said:

I can never remember an SE being involved

Probably because the folk had loads of experience and understood the materials they were using. Sadly in the modern world this is often no longer the case.

 

On 05/03/2025 at 11:29, SteamyTea said:

I can never remember an SE being involved,

Do you know if these buildings have fallen down? Mind you they may have masive cracks in them?

 

[SteamyTea]

4 hours ago, Gus Potter said:

Do you know if these buildings have fallen down

No idea, I think I would have heard if they had failed badly.

St. Mary's Hospital Walkway was removed after about 30 years of usage, but that was part of a total redesign.

The Mosque dome had higher powers keeping it up.