Self-build in Perth & Kinross - hello

[Kelvin]

Yep. It’s all in the garage ready to go on

[Thorfun]

3 minutes ago, Kelvin said:

Yep. It’s all in the garage ready to go on

it's interesting. ours was fitted in the factory so we had protection from the elements as soon as each panel went up. i would've thought that in Scotland where the weather is changeable the membrane would be put on in factory. i presume that the OSB is left to dry out before the insulation is pumped in to the walls?

 

it's fascinating to see how different companies do it different ways. i'm loving following your journey, keep up the great updates! although, i must criticise  a little as personally i'd like more photos and timelapse video footage! 🙂

[Kelvin]

They weren’t keen in being video’d neither the garage guys nor the kit guys as that was my plan. It’s understandable for reasons I won’t go into here! 
 

I asked that question myself ref the breather membrane. They have tried it apparently but it’s too easy to damage it so they prefer to do at the end. It will need to dry out. Most of the walls are actually pretty dry. The focus for the next couple of weeks is to get the plywood decking on the roof, rooflights in then roofs on. 

[Thorfun]

1 minute ago, Kelvin said:

They weren’t keen in being video’d neither the garage guys nor the kit guys as that was my plan. It’s understandable for reasons I won’t go into here! 
 

I asked that question myself ref the breather membrane. They have tried it apparently but it’s too easy to damage it so they prefer to do at the end. It will need to dry out. Most of the walls are actually pretty dry. The focus for the next couple of weeks is to get the plywood decking on the roof, rooflights in then roofs on. 

interesting about their lack of wanting to be video'd! surely it has nothing to do with them if you want to video your site. besides, video is important for site safety and security. I am a paranoid git though and so my mind says what have they got to hide!!! 🤣

 

if they have their reasons and you were ok with them and don't want to go in to then I fully respect your choice. I still want more photos though. 😉 

[Dunc]

4 minutes ago, Thorfun said:

I still want more photos though. 😉 

+1 🙂

Looking really good! I had thought the garage looked quite big before the house went up, now it looks dwarfed!

[Kelvin]

I have loads of pictures so will add them once the kit is up to show some of the specific details. 
 

I even bought a spangly new GoPro and upgraded the firmware specifically for doing timelapse. I could have insisted but I could see by their body language they weren’t keen so didn’t push it. 

[Kelvin]

4 minutes ago, Dunc said:

+1 🙂

Looking really good! I had thought the garage looked quite big before the house went up, now it looks dwarfed!

All along my other half has been saying the garage is too big. However I kept saying it will be fine. It’s 10.5m long so about as long as the house is wide so my view always was they would be in a nice proportion. 
 

The porch is the widest and longest porch they’ve done. They are going to encourage other clients to do similar width wise as the standard porch is too small to be practical. 

[JamesP]

@Kelvin Great project, photos and detail.

Is this a Hebhomes build and is the roof a cold or warm roof, wondering if OSB counts as insulation or sarking?

[Kelvin]

Yes it’s an LH702PD Heb Home that we’ve made some amendments to increasing the floor area by 35m² 

 

It’s a warm roof. The OSB is used as sheathing to close the panel. I think sarking and sheathing are much the same thing. We’ll batten this then deck with 18mm plywood. The difference between this and their SIP panels is ours has those big space joists in the roof whereas the SIP builds use roof cassettes I think they call them. 
 

One question that did arise today is how to fit the windows. The architect wants them flush with the kit which creates quite a big external reveal with our board on board cladding that then needs to be closed up. Both joiners on-site said this was a mistake and causes a lot of problems trying to fit them in their experience. Their view is you want it more flush with the cladding. 
 

While this is a kit it’s more a hybrid as there’s been a bit of stick building on-site too. 

Edited April 27, 2023 by Kelvin

[Iceverge]

It's a tricky one this. 

 

Thermally they'd be best in the center of the twinwall frame and the frames covered by some EWI of some kind. Windows frames are by far the weakest point of any build. 

 

Moving them to the outside of the kit is only marginally worse but hovering them outside the kit is thermally weak. @TerryE did this but surrounded with Rockwool socks which buys a lot better detail. 

 

 

However your priority must be to keep the rain at bay. I've pondered over this lots for twinwall timber frame. 

 

Questions

 

Do the windows open in or out?

What kind of sills are you using? 

What windows are you using?

What is your cladding makeup? 

 

 

[Thorfun]

1 hour ago, Kelvin said:

One question that did arise today is how to fit the windows. The architect wants them flush with the kit which creates quite a big external reveal with our board on board cladding that then needs to be closed up.

This sounds like how we did ours. Our chippie had no issues with the reveals although ours isn’t board on board, we’ve vertical tongue and groove and only 140mm TF with 80mm PIR internal to that. But we used 50mm x 50mm battens and counter battens so our external buildup is about 120mm. 
 

let me know if you want pictures. 

Edited April 27, 2023 by Thorfun
Added external build up size

[JamesP]

From my limited experience as a first time self builder my wall build up was about 425mm. I put the windows 110mm in from the cladding and EWI (Pavatherm) and lined the inside of the reveals with 20mm Pavatherm.

Would you be able to share any drawings of wall and roof build up?

[Kelvin]

Thanks all. 
 

@Iceverge windows open in, timber sills (if that’s what you mean), Nordan Ntech 3G windows, cladding is board on board (150mm x 22mm) on 38mm x 50mm horizontal battens and 19mm x 38mm counter battens

 

@Thorfun Yes pictures would be helpful 

 

@JamesP see below. 
 

Windows being installed next week. 
 

 

 

[Dunc]

I'm not sure I understand the joiner's problem?

It seems pretty clear in the plans, other than need to support the "outside" cladding board adjacent to the window reveal by increasing thickness of final batten (and the mis-labelling of #5 in the head section view).

 

[Kelvin]

It seems clear to me too. I’ve printed off the construction drawings and will discuss today. 
 

There’s loads of mislabelling. I gave up correcting it and sending it back them. 

[Iceverge]

2 hours ago, Kelvin said:

timber sills (if that’s what you mean)

 

Externally? 

 

 

[Iceverge]

 

This detail lifted from the lovely old Holloway passivhaus. 

 

https://passivehouseplus.ie/magazine/new-build/deep-green-passive-house-defies-all-weather

 

Hopefully you can enlarge it enough. 

 

It differs slightly in the continuous layer of external insulation you don't have but the bit covering the frame is the most important. 

 

You could use EPS instead of Woodfiber for over insulating the frames. They used an insulated aluminium sill. 

[Iceverge]

 

This bit is the important bit for the jambs and head. 

[Iceverge]

 

Here's a window head. See what you think. I'll do the membranes and tapes next. 

[Iceverge]

This is simplified actually. 

 

No need for the 19mm Battens to run so far down. 

 

 

Suggested sequence.

 

1. Install 18mm window boxes. 

2. Install Windows 100mm back from the outer edge. 

3. Tape the windows to some breather membrane and return to the outside of the sheathing. 

4. Screw the 150x57 timbers in place as shown. Use this to line up to the corners of the window to ensure a consistant amount of frame will be exposed later. 

5. Push fit some EPS insulation. Ensure it is a snug fit. 

6. Apply the window head trim as shown with SS screws. 

7. Finish the breather membrane overlapping as shown to ensure all drips go to the outside. 

 

 

[Iceverge]

r

 

 

 

 

 

Have a look at the images above. It's a pretty crude representation of a window one properly in Therm would take me until 2050. 

 

What you can see is the effect of the reduction in heat loss through the header by moving the window inside it and by adding some external insulation to the frame . Like I say the window frames are thermally weak even on excellent windows. You can only do so much.  

 

 

[Kelvin]

This is really helpful. Thank you 

[TerryE]

@Kelvin you can see my window profiles on my blog: Window and Door Detailing.  I could take this route of moving my frames out to the outside of the TF because we had an outer stone skin, and we'd spec'd the TF with 60° inner reveals.  This all worked well for us and gave the house a fairly light and airy feel despite the planners limiting window sizes to conform to "local cottage style".  No probs after being in for nearly 6 years now. Works well in terms of weatherproofing, airtightness and thermally.  Whatever approach you adopt you need to make sure that you address all three of these aspects.

 

My first reaction to your TF is that it is similar to by MBC TF -- except that the panels seem inside-out.  For the MBC profile, the OSB racking is plasticised and on the inside.  This forms to VCL and has a battened out service cavity within it.  The outer covering is panelvent with is breathable.

 

OSB is sufficiently moisture and air tight to form a decent VCL, so if you have inner vapour barrier then you will get moisture problems over time as the frame and the internal insulation needs to breath.  Perhaps you should clarify your breathing + airtightness + thermal design to make sure these points have been properly addressed otherwise you could have real problems in 5-10 years time.

 

Where is your air-tightness barrier?  You are going to have a lot of service penetrations, so you need to have a strategy for these as well.  We plan all of ours ahead of time and used the appropriate sized ABS pipe to span the frame.  We taped up these ourselves.  The trades could then easily route pipes / cabling through these as needed, and the foamed and silicon-sealed these immediately before the airtightness test.  Passed on first attempt.

 

One last point.  We used a riven slate covering on our entire slab.  Jan got it from the Mrs-stone store online.  No probs in procuring, price or laying.  This was really cheap on it only took the tiler a few days to lay.  No probs since either.  We still like it.

Edited April 29, 2023 by TerryE

[Kelvin]

@TerryE what do you mean by inside out? The Sterling OSB3 boards aren’t sided. There will be an external breather membrane with Corotop Blue on the roof and Glidevale Protect 5000 on the walls. Internally there’s an air tight membrane using Protect VC Foil Ultra then a 25mm service cavity is formed. 
 

We’ve minimised service penetrations as much as possible as most of the ins and outs are through ducting under the foundation slab. We’ll have to penetrate the wall/roof for external wall lighting, MVHR, the SVP and hot water cylinder emergency release piping. 
 

Reference your air tightness test passing first time. I would hope so given the regs don’t set a very high bar. What was your final result? 

Edited April 30, 2023 by Kelvin

[Iceverge]

On 29/04/2023 at 12:49, TerryE said:

OSB is sufficiently moisture and air tight to form a decent VCL, so if you have inner vapour barrier then you will get moisture problems over time as the frame and the internal insulation needs to breath.  Perhaps you should clarify your breathing + airtightness + thermal design to make sure these points have been properly addressed otherwise you could have real problems in 5-10 years time.

 

I think the risks of using OSB as sheathing are overblown. Most vapour moves via holes and currents of air rather than diffusion. If you do a top job of an airtightness anywhere in the wall and don't put in layer of completely impervious layers like polythene and foil faced boards you should be ok.

 

If you stick in layers of foil faced boards with loads of gaps and a polythene VCL with lots and lots of holes then I think its a recipe for disaster.   

 

A little bit click baitish this title but the content is OK.