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Posted (edited)

Good evening all,

 

Groundworks started on my new build here in Hamilton this week - it's all started to move pretty quickly now and feeling quite real for a change! I am kind of project managing myself but with the bigger items being delegated. 

 

Foundations are in but need to be changes slightly to accommodate the floor - (thermabeam with 0.11 u value) and I am just awaiting load calcs ok before ordering as we had some really high line lods on some of the racking walls owing to the open plan nature of the house. Provided everything goes well the floor should be here in a few weeks and is supplied and fitted.

 

I have a friendly electrician and plumber who are going to take care of the plumbing/UFH and electrics.

 

The main outstanding matter at this time is that of the supply and erection of the kit - i have 2 quotes - one from a local kit guy and one slightly further away but which is a bigger operation. The one further away is a bit cheaper all things considered but I feel there are perhaps advantages with the local guy as well him and his team are local so any issues etc can be resolved quicker and if not I can go chap his door! He seems a bit more flexible too as he's a smaller operation than the one thats an hour and a half up the road.

 

If I was to go with the local guy he has included in his quote 1st fix, 2nd fix and ironmongery but not listed exactly whats covered by this. Is there anything else I should be negotiating to make sure is part of his quote. The installation of the stairs, windows and kitchen (all supplied by me) have all been costed already and we have agreed a guarantee on the air tightness (tested to better than 3 ach). I know not as good as a lot of the build on here but when i looked at passive standard builds the cost was almost doubling!

 

So I there anything else i should be raising with him to make sure its included as part of his work or anything that can be open to interpretation as what is 1st or 2nd fix?

 

 

Edited by osmononame

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Get as much detail as possible 

Ie windows and doors plaster-boarding digits gutters 

You May find that one has included some or all of these and the other hasn’t 

2-3 on the air test is easily achievable even on a mass produced brick and block house 

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Thanks. I will add gutters to the list! Didn't even occur to me about those!

 

As far as air tightness is concerned if 3 is too easy a target for the air test what would be something that is achievable without any (or at least not much) extra cost?

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Posted (edited)

Hi, I believe you must be pretty near us, we built our third house in 2018/2019 although we still have landscaping and driveway to finish. Would be happy to talk to you if there’s anything you feel unsure of.

with regards to your 1st fix etc

1st fix is usually the kit erection including doors and windows , ours also included soffit and fascia installation 

2nd fix would be internal partitions, insulation, plasterboarding and any flooring which is not concrete 

3rd fix or finishing was all other internal joinery work(doors, skirting, staircase, windowsills and wardrobes.

Edited by Christine Walker
Additional information

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hi, are you sticking with standard 145mm kit or trying to get a better u value? even with a standard kit, if you internally clad in osb such as propassive glued to kit and glued joints, you could acheive a good level of airtightness and then have a service cavity. realistically it shouldn't cost double for the kit to passive standards. price the fitting of the insulation (neatly done to avoid cold spots) against blown insulation and i don't think there will be much difference.

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1 hour ago, Christine Walker said:

Hi, I believe you must be pretty near us, we built our third house in 2018/2019 although we still have landscaping and driveway to finish. Would be happy to talk to you if there’s anything you feel unsure of.

with regards to your 1st fix etc

1st fix is usually the kit erection including doors and windows , ours also included soffit and fascia installation 

2nd fix would be internal partitions, insulation, plasterboarding and any flooring which is not concrete 

3rd fix or finishing was all other internal joinery work(doors, skirting, staircase, windowsills and wardrobes.

 

Thats useful Christine - thanks. From looking at my guys quote the 3rd fix is included within the 2nd fix as he has all those items listed.

 

25 minutes ago, Simplysimon said:

hi, are you sticking with standard 145mm kit or trying to get a better u value? even with a standard kit, if you internally clad in osb such as propassive glued to kit and glued joints, you could acheive a good level of airtightness and then have a service cavity. realistically it shouldn't cost double for the kit to passive standards. price the fitting of the insulation (neatly done to avoid cold spots) against blown insulation and i don't think there will be much difference.

 

Yes - sticking with a standard 145mm kit I am afraid - I got quotes for 190mm kits and MBC twin frame and honestly it was crazy costs compared to the 145mm we had spec'ed. It really wasn't worth it for us to look at anything past 145mm with the budget we have. Currently the make up of the wall is as follows:

 

9 mm OSB sheathing /w membrane.
140 mm mineral wool insulation
50 mm PIR foil faced insulation board inside walls.
Airtight vapour control layer and joint tape inside walls
Service void
Plasterboard

 

All in that order. Are you saying if we replace the airtight vapour control layer membrane with the glued propassive osb we should get a better airtight layer (all other things being equal)?

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Posted (edited)
14 minutes ago, osmononame said:

 

Thats useful Christine - thanks. From looking at my guys quote the 3rd fix is included within the 2nd fix as he has all those items listed.

 

 

Yes - sticking with a standard 145mm kit I am afraid - I got quotes for 190mm kits and MBC twin frame and honestly it was crazy costs compared to the 145mm we had spec'ed. It really wasn't worth it for us to look at anything past 145mm with the budget we have. Currently the make up of the wall is as follows:

 

9 mm OSB sheathing /w membrane.
140 mm mineral wool insulation
50 mm PIR foil faced insulation board inside walls.
Airtight vapour control layer and joint tape inside walls
Service void
Plasterboard

 

All in that order. Are you saying if we replace the airtight vapour control layer membrane with the glued propassive osb we should get a better airtight layer (all other things being equal)?

 

I'm no expert and haven't even started building our house yet as we're still waiting on planning permission! but I have had numerous quotes for open panel 140mm timber frame with the idea of fitting the insulation myself to save a substantial amount of money.

 

the external wall makeup you've got there should yield about 0.14W/m2K and is pretty much the exact same make up I'm looking at doing but I might stretch to 80mm of PIR which would take it to about 0.12W/m2K.

 

I'm still not sure about using the propassive osb instead of the VCL as I'm sure you can get excellent air tightness just using the VCL. I guess the propassive has less risk of someone piercing it and creating a hole in your nice airtightness layer when running cables and pipes etc.

 

as such, I'm going to be eagerly watching this thread so I can read what those who actually know what they're talking about say!

Edited by Thorfun
fixing stupid autocorrect

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Posted (edited)

the benefit as i see it is that it's better racking strength, can't be punctured easily and if neatly cut and fitted should be equal to, or better than, poly. for air tight. what is the u value for your wall? have you looked at buying i beams and stick building?

how are you fitting joists, sitting on wall head or hanging? if sitting on wall you can fit poly around the ends and achieve good air tighness as others on here have but propassive right round and hang them is a lot easier.

Edited by Simplysimon
extra question and cross post for u value

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Anyone I have tried locally to quote on an i beam wouldn't as they have never done such a build. I am sure I could have it designed and they can build it but even knowing the cost differential between 145mm and an I beam would help. I just couldn't find one!

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Posted (edited)

Just out of interest what kind of price per square metre did the further away kit come in at?

 

We are about to do a build with the same wall spec for my parents in Edinburgh. I had a couple of quotes from Scotframe and MBC. I reckon MBC were about 15% more expensive than Scotframe once I had adjusted for the difference between the quotes. MBC is around £450 a square metre including the roof insulation to 0.1, or about £400 ex the roof insulation.

 

As to your question I would get a detailed list, because different people could easily include different things in first, second fix etc and you don't want to have to argue about it later.

 

If you run the numbers on heat requirement for a house there is very little difference between 0.14 and 0.12 u-value. In our case we have a width restriction so I am sticking with 0.14. The extra budget might be better used for the windows where it is likely you can get a bigger uplift.

Edited by AliG

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I have not done an apples to apple comparison between the MBC twin frame system and a regular build but my house is 356m² over ground, first and second floors. MBC's quote for the twin wall was £162,000 supplied and erected (just the kit - not including the foundations). Doing it with the local guy is working less than £100,000 (around £95,000 but depends on some of the materials which I haven't costed yet) but that includes supply and fit of kitchen/windows/staircase/doors (internal and external). Even if I was to 'upspec' the build I wouldn't get anywhere near MBC's quote which doesn't include, second fix / finishing / installation of windows and doors (although i will need to check on the last point). Their costs for the foundations were a lot higher than i can get locally at 0.11 u value for the floor. MBC's kit comes with posi joists - my one is spec'ed with JJI - thats a £2k difference so like i said not apples to apples but MBC was far enough away for it not to be in contention as soon as the quote came through.

 

There is no doubt that the product is spot on with MBC and a 0.6 ach air tightness and u values they guarantee are hard to beat - I just couldn't justify it with the cost and not only justifying it but being able to afford it (which I can't!).

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25 minutes ago, osmononame said:

Anyone I have tried locally to quote on an i beam wouldn't as they have never done such a build. I am sure I could have it designed and they can build it but even knowing the cost differential between 145mm and an I beam would help. I just couldn't find one!

We're a bit further north than you, getting to the end of our build. We used I beams, stick built on site.

To give you a rough idea of price differences on raw materials:

 

A 12m length of 300mm JJI A I beam was about £70 for us as I recall.

Today I picked up a 4.8m length of 6 x 2 for £2.10/m, so around £25 for 12m.

 

These are not the most competitive prices. We wanted a thicker wall with blown insulation, and the I beam allows us to do that relatively easily. There is not much difference in the framing/frame design.

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7 minutes ago, osmononame said:

MBC's quote for the twin wall was £162,000 supplied and erected (just the kit - not including the foundations).

 

Just looking at our quote, the twin wall is another 20% more expensive than 0.14 u-value walls and the 0.1 u-value blown insulation roof. I couldn't see much justification, it would be lucky to cut £10 a year off the heating bill.

 

I did wonder about the better racking strength of the 300mm wall and the sound insulation, but you get some of those benefits from using the blown cellulose roof and the combination of mineral wool plus PIR in the walls should do a pretty good job. It was also just too thick a wall in our case. My last house was around 17 years old and only had a 90mm kit with mineral wool plus a rendered block skin, so the 0.14 wall is already a massive improvement on that.

 

Your price does seem very cheap once you take out the windows, kitchen etc you must be looking at around 65k for just the kit, so about half the price of a similar spec MBC kit.

 

 

 

 

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Yeah. The price seems good. I think I'm going to go with the local guy but have a few points to clarify with him before I commit. I'm trying to get him to include the cost of the MVHR (running of ductwork at least) within the quote. With jji joists I am sure he will have his work cut out (trying to avoid posi joists if I can due to budget!). 

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