Self-build in Perth & Kinross - hello

[TerryE]

@Kelvin I was posting on another thread on this same topic and sometimes get my wires crossed, but my comment also apply on this thread:

As I describe in this post, by inside out I was talking about OSB placement: whether it is on the outside face of the TF or inside.  As it happens our external-facing OSB3 is sided because has a green plasticised surface to ensure airtightness., but TBH if you've left a bit of exterior grade OSB out in the elements for a year or so it is pretty damn waterproof and airtight too so an integral layer will form a decent ATL.  The issue as I see it that at least one side must be properly breathable.  It is a debate as to whether this is better on the inside or out. 

[Furnace]

9 hours ago, Iceverge said:

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

@Iceverge

Is he saying that any internal barrier is unnecessary because the external barrier is so airtight that air/vapour doesn't migrate from inside to the cold sheathing on the external side of the frame?

[Iceverge]

3 hours ago, Furnace said:

@Iceverge

Is he saying that any internal barrier is unnecessary because the external barrier is so airtight that air/vapour doesn't migrate from inside to the cold sheathing on the external side of the frame?

 

Yes. The cellulose helps too because it fills all the voids. I wouldn't try this with board insulation. 

 

It's relatively common in the US to have an external air barrier and they can get much colder winters than us heightening the risk of condensation on the sheathing. 

 

 

[Furnace]

31 minutes ago, Iceverge said:

It's relatively common in the US to have an external air barrier and they can get much colder winters than us heightening the risk of condensation on the sheathing

@Iceverge It seems like it's a more nuanced issue than one might imagine. My original thinking had been that it was important to prevent moisture laden internal air from getting into the insulation (making it damp and perform poorly) and to contact the cooler internal surface of the external wall (causing condensation that cannot escape). That video suggests that possibly the water vapour does not penetrate through the insulation so cannot condense on the internal surface of the external wall, or that it happens only a small amount, and dries out when the external temperatures rise?
My instinct (probably wrong) would be to put on the inside of the insulation a membrane that was both vapour-proof (to prevent any moisture passing from inside the house into the insulation) and air-proof (to prevent warm air leaking out). On the outside of the external wall place a membrane that was airtight (to prevent cold air penetrating into the insulation), but also vapour permeable (to ensure that any moisture that did make it into the insulation had a path to exit)
The chap in the video seemed to think that two membranes were unnecessary, and his experience to date appears to support that view.

Which approach would you use if building again?

Edited May 1, 2023 by Furnace

[Iceverge]

I think it shows that almost all moisture problems come from air currents through the wall caused by bad airtighess. 

 

Normally in heating climates we put our air barrier inside most or all of the insulation. It's considered safer but I think that only applies when you are planning on doing a poor air sealing job and air will be moving through the build-up 

 

What's almost always neglected is the importance of a windtightness layer that stops air blowing through the insulation at the outside. Moving the airtighess layer to the outside takes care of both of these and as the wall can dry properly both inwards and outward it's a good solution. 

 

It'll be difficulty to change people's thinking though.

 

@IanR has a unusual approach. Plasterboard, ijoists with cellulose,and a woodfiber racking board taped for airtighess. It's a nice system. Minimum components. Airtightness layer away from the trades. Plenty of service space. The wall can dry both directions and he got an phenomenal airtighess result. 

 

 

 

 

 

 

 

[Kelvin]

Quick question. Is it normal to fit the non-structural internal partitions before the floor insulation and screed install? I get they needed to do the structural partitions. The reason I ask is it’s not actually in the contract to do it so was surprised to come down to site tonight and see them fitted. 

[saveasteading]

44 minutes ago, Kelvin said:

 

46 minutes ago, Kelvin said:

internal partitions before the floor insulation and screed install

 

With a full package, the contractor won't want to have a return visit after the screed is down, so this makes sense.

You would be paying for it.

Another advantage  is they can fix the plates down to the slab..a very bad idea into screed esp if with UFH.

 

and even though not designated as structural walls, they don't know that and are stiffening up the whole building.

 

It might complicate an ufh layout, but probably not.

 

pouring screed through a stud wall, you know where it will crack but have crack inducers therefor tidiness.

[Thorfun]

On 28/04/2023 at 08:24, Kelvin said:

@Thorfun Yes pictures would be helpful 

sorry for the delay in responding. been busy on our house trying to get ready for the liquid screed. you've had loads of great advice so I'm not sure how useful these will be but here are some photos of a reveal without cladding and then with cladding. 

 

[TerryE]

On 01/05/2023 at 18:08, Kelvin said:

Quick question. Is it normal to fit the non-structural internal partitions before the floor insulation and screed install?

This depends on the type of slab you have.  We had an MBC warmslab which is n × 50mm MOT 3 layers, each individually compacted followed by 50mm sharp sand compacted and refilled to 50mm; the EPC "jelly-mold" with the UFH piping fitted to the rebar within the jelly-mold then a single poured slab which covered the entire ground floor and which was spin floated and polished flat.  (The biggest deviation across the entire slab was ~3mm slump along one exterior wall.  The TF and internal partitions were erected on this after it had cured for 2 weeks.  We then covered the entire floor with a riven slate as part of second fix (and the tiler took out the slump; he said it was the flattest squarest floor that he had ever covered).

 

If you have a more conventional profile where the UFH and screed is laid as part of second fix then the internal partitions typically go in first and levelling goes from room to room.  However, whilst the screeders will typically get the individual rooms pretty flat, you will often get left with a few mm ramp across door openings, as it they have to work towards a central hallway for rooms without an external door / means of escape.  They will rarely get two separate rooms to the same FFL within 3-5 mm unless they are really good. 

 

If yours is in this second category then make sure that they give a room by room execution plan and exit / link strategy, because if you do have FFL jumps between rooms then you will at best get a shrug and "it happens".  

 

If you are erecting the (non-loadbearing) internal partitions yourself then I suggest that it is better to screed first, but others might take a different view.  🙂 

 

 

   

Edited May 4, 2023 by TerryE

[Kelvin]

Thanks for all the comments. Been a bit busy on-site these last few days plus more damage. For reasons best known to the kit erection guys one of them did this. 🙄 Why he put a screw through there I’ve no idea. 

 

[Thorfun]

Something Magic Man can fix? Get the TF company to pay. 

[Kelvin]

I realise it’s a minor thing but it’s the carelessness that’s pisses me off and the subsequent hassle it causes getting it fixed. So far all the damage should have been avoidable with just a bit more care. 
 

Meeting tomorrow with the company owner to go through the defects list. He’s confident his detail guy can sort it. I owe them the retention percentage which I’ve said I’m not paying until all the defects are resolved. 
 

The bigger problem we have is  I think the windows have been fitted a touch too far in. They are in line with the kit as per the construction details but I can’t see how the cills can be clipped into place. We tried to fit one today and couldn’t get it to clip in. The kit company are due back next week to finish off so I’ll get them to fit a cill to see if they can do it. 
 

My follow on joiner isn’t impressed with their attention to detail. He’s pointed out a few things that could have been done better. Basic stuff. He said he’ll fix it. Although he’s impressed with the kit overall. 
 

One observation. I was on-site at 6.30 this morning tidying up and removing the carnage the kit guys left behind. The house was surprisingly warm. It’s got no insulation and the windows aren’t sealed up yet. 

[Kelvin]

How many nails and screws get dropped on the average build? I could open a hardware store! 

[saveasteading]

1 hour ago, Kelvin said:

How many nails and screws get dropped on the average build? 

4%.

[Kelvin]

What a battle this self-build malarkey is. Load of builders in yesterday. Why are you putting so much insulation under the screed we only ever do 100mm next to nothing is lost to the ground you’re wasting your money. 
 

Why did you insulate the steels? Another waste of money. 
 

You don’t need insulated plasterboard 

 

If you wanted to build a passive house why didn’t you just do that…because it’s not a passive house it’s just a well insulated house. 

 

Also twice I’ve had to pull wet insulation out of the walls. Last night I was on-site until 10pm having started 6am re-doing all the upstairs insulation. After explaining I don’t want any large air gaps because they’ve cut it too short and cba filing in the gap. Unfortunately I was so knackered I didn’t handle this conversation with the builders very well. I planned to calmly tell them what was wrong and why instead I ranted at them. I apologised later though. 
 

Add some missing steel for upstairs holding the glulam up, a kit fabrication error making the flat roof section 60mm too high where it adjoins the pitch roof, incorrect centre posts for for the rooflights, and several other omissions from the construction pack that’s only obvious to me now the house is up. I am rather (expletive deleted)ed off and tired! 😂 

[Thorfun]

31 minutes ago, Kelvin said:

What a battle this self-build malarkey is. Load of builders in yesterday. Why are you putting so much insulation under the screed we only ever do 100mm next to nothing is lost to the ground you’re wasting your money. 
 

Why did you insulate the steels? Another waste of money. 
 

You don’t need insulated plasterboard 

 

If you wanted to build a passive house why didn’t you just do that…because it’s not a passive house it’s just a well insulated house. 

 

Also twice I’ve had to pull wet insulation out of the walls. Last night I was on-site until 10pm having started 6am re-doing all the upstairs insulation. After explaining I don’t want any large air gaps because they’ve cut it too short and cba filing in the gap. Unfortunately I was so knackered I didn’t handle this conversation with the builders very well. I planned to calmly tell them what was wrong and why instead I ranted at them. I apologised later though. 
 

Add some missing steel for upstairs holding the glulam up, a kit fabrication error making the flat roof section 60mm too high where it adjoins the pitch roof, incorrect centre posts for for the rooflights, and several other omissions from the construction pack that’s only obvious to me now the house is up. I am rather (expletive deleted)ed off and tired! 😂 

All sounds very familiar. I do love the way your builders are in fact thermal engineers and I presume they showed you the complicated calculations proving their bold statements? 😂
 

Our entrance hall roof was built 100mm too low. Only noticed it when I came to try and add the 100mm PIR under the trusses!! Way too late to do anything about it then! We just adapted and moved on. 

Edited May 18, 2023 by Thorfun

[saveasteading]

2 hours ago, Kelvin said:

. I am rather (expletive deleted)ed off and tired

Whereas these builders have the blessing of ignorance, thinking they are skilled and knowledgable, and that Engineers and Architects overdesign.

You are a mere client.

There isn't much hope other than insist it is as drawing. They probably fear the bco, and withholding payment of course.

 

Remember that their instinctive reaction to any criticism is to invent an excuse, any excuse. It works often enough as most clients don't want a fuss and fear losing the builder.

 

Stay strong.

[saveasteading]

On 16/05/2023 at 17:21, saveasteading said:

On 16/05/2023 at 15:42, Kelvin said:

How many nails and screws get dropped on the average build? 

4%.

Was I the closest in this quiz? 

[Iceverge]

@Kelvin it's early days. Believe me I've been there. To see a project you've poured your heart and soul and all your money into being tarnished is gutwrenching. 

 

However something will give if you don't change tack. 

 

The budget , the quality, the schedule,  or your health. A little bit of the last three for me.

 

The schedule and the budget are definitely the best places to compromise. Too many of us have poor quality houses or have been driven to mental breakdowns or ambulances.

 

 

 

 

 

 

 

 

 

 

 

[Kelvin]

32 minutes ago, saveasteading said:

Was I the closest in this quiz? 

well it’s a shedload! 😂 

 

This is what was left behind by the garage people. 

 

[Kelvin]

The other gripe I have is how long it’s taken the ‘kit’ builders. We are on week 5 with another week to go plus two weeks to build the kit at the factory. The HH programme they gave me was 2  weeks on-site. I didn’t believe that so planned for 3 to start the follow on trades. It’s not held us up but I really do need them out by end of next week so that I can lay the floor insulation. Their SIP kits take about 9 the guys told me. While ours is technically a kit there’s still a lot of joinery as well. It’s really a hybrid space frame system. It will be 70 man days on site plus another say 15 to manufacture the kit. My rough maths says they’ve blown through the kit erection price they charged me (£20,000) 
 

 

[Carrerahill]

5 hours ago, Kelvin said:

"...we only ever do 100mm..."

I hate this attitude. I deal with it on a weekly basis professionally and often enough when I dare let someone do work for one of my projects which is rare because even the "good ones" are never that good and usually fall foul of my high, but reasonable standards at some point, I think my plasterer might be the only one I think scores a high 90%, oh and my brickie 98%.

 

When contractors are tendering projects they often hit us with TQ's/RFI's to help them with their laziness (often because they don't read notes, look at details or schedules or read the spec) and I have become so used to reading, "Normally..." or "The way we do it..." - I quite often respond with, just because it has been done that way in the past doesn't make it right.

 

The "normal" or "usual" way for them is always the cheapest or easiest route, it's all driven through being lazy and cheap. 

 

They often just see something that looks like it will cost a bit more than usual and try and remove it, what they don't take into account is all the time and effort that goes into designing things, I have come to the conclusion that they are all ignorant or lazy/cheap. 

 

So back to your insulation, maybe 100mm is the norm, but your situation is not normal, you are a owner/builder who wants your house better than what you can buy off the shelf, hence the more onerous standards, why they treat these improvements with contempt is the bit that really grinds my gears. 

 

Most contractors would think most of us are mad they way we do some of the detailing and additional steps in our builds. 

 

 

Edited May 18, 2023 by Carrerahill

[Carrerahill]

20 minutes ago, Kelvin said:

 

 

Is that a Husky 435 by any chance?

[Kelvin]

It’s a 440. Brilliant bit of kit. 

[Kelvin]

They keep referencing this other house they are doing nearby so I went and had a look. The owner was there so he let me have a nose around. It’s a big place, bigger than mine. Bit more complicated layout. However really poor detailing in terms of insulation, thermal bridging, build ups etc. Turnkey build. He has zero involvement. Wasn’t even sure of room layout etc. I didn’t say anything obviously. Mine is about as good as I could have made it given my lack of knowledge at the start. It could have been better though.