Most affordable/recommended holistic approach to a new build

Brave Harvey

Hi there, just a question to put forward there as my brother is at planning stage with his 2 storey 250m.sq. house.
He plan's on using a stove/back boiler but as far as every thing else he is at sea. He will be getting a preliminary Ber done soon to see where he is at. He is planning on the internal slabs and I am lobbying him at the moment to keep his insulation in the one layer.
The professional he is using has him convinced to use the slabs! Says he will run up his costs if he goes with a deep cavity, with the expense of the wall ties and cavity closers..
There is a small stream running by the proposed house which will be piped, there is always a good flow of water in this stream and wonder is there any type of renewable system that could utilize this??
Another professional has convinced him to steer clear of MHRV as they are bad news. I am also lobbying him on this as I believe that it goes hand in hand in airtightness and in 5 years down the line he will have a house that is outdated when they become compulsory.
ANY help would be appreciated..

MicktheMan

Brave Harvey wrote: »

Hi there, just a question to put forward there as my brother is at planning stage with his 2 storey 250m.sq. house.
He plan's on using a stove/back boiler but as far as every thing else he is at sea. He will be getting a preliminary Ber done soon to see where he is at. He is planning on the internal slabs and I am lobbying him at the moment to keep his insulation in the one layer.
The engineer he is using has him convinced to use the slabs! Says he will run up his costs if he goes with a deep cavity, with the expense of the wall ties and cavity closers..
There is a small stream running by the proposed house which will be piped, there is always a good flow of water in this stream and wonder is there any type of renewable system that could utilize this??
A builder has convinced him to steer clear of MHRV as they are bad news. I am also lobbying him on this as I believe personally that it goes hand in hand in airtightness and in 5 years down the line he will have a house that is outdated when they become compulsory.
ANY help would be appreciated, give me more ammo against the so-called professionals!!

Ask your brother does want to live in a draughty house which will need minimum 2 to 3 tons of oil each year to keep warm with no heat retention and a high risk of mould growth or a house which needs a tenth of this, no draughts, good heat retention and fresh indoor air (low mould risk).
If the former, then, go ahead with his plan.

On the costs side, has he or his engineer done the sums of material/labour cost of internal slabbing vs wider cavity and good thermal bridging detailing?
I would advise him to seriously seek out other building professionals who have a more progressive attitude.
Finally, as somebody who makes his living from testing (a lot of new) houses for heat loss mechanisms, let me share with you the most common comments made to me by clients "if only we had spoken to someone like you before we built".

heavydawson

Brave Harvey wrote: »

Hi there, just a question to put forward there as my brother is at planning stage with his 2 storey 250m.sq. house.
He plan's on using a stove/back boiler but as far as every thing else he is at sea. He will be getting a preliminary Ber done soon to see where he is at. He is planning on the internal slabs and I am lobbying him at the moment to keep his insulation in the one layer.
The engineer he is using has him convinced to use the slabs! Says he will run up his costs if he goes with a deep cavity, with the expense of the wall ties and cavity closers..
There is a small stream running by the proposed house which will be piped, there is always a good flow of water in this stream and wonder is there any type of renewable system that could utilize this??
A builder has convinced him to steer clear of MHRV as they are bad news. I am also lobbying him on this as I believe personally that it goes hand in hand in airtightness and in 5 years down the line he will have a house that is outdated when they become compulsory.
ANY help would be appreciated, give me more ammo against the so-called professionals!!

Depends on how deep you go with the cavity. I've gone 150mm, which you could hardly call deep and used a full fill solid 150mm board in the cavity.
To achieve the same u-value, for a pumped bead cavity, you'd need to be going to 225mm or greater. Things start getting expensive then and practicalities like block-layers ability to lay blocks at a stretch.
We're also putting in MHRV, but if I'm not mistaken, people have suggested here that air-tightness becomes a issue at the slab joints when using insulated slabs.

Again, just from the general discussions here on boards, you're existing advice to him is sound. Single insulating layer, good airtightness (<1ach/hour), and MHRV. Sound like an engineer who's either too lazy or stuck in their own ways to invest any effort in your brothers house. You might be better off finding another one for him

sinnerboy

Most engineers are not up to speed with wide cavity construction design in my own personal experience. So one finds a de facto / default max cavity of 150mm in a lot of cases. So the most high performing bead fill in a 150mm cavity is probably the "default max" and thus the need for "the slabs" - a convenient build method which saves the builder a lot of first fix chasing but costs the costumer in build quality. In term of quality of build this is where it pays to seek out upskilled up to date professionals to attempt the wider cavity.

Comments the builder has made about HRV would ring alarm bells with me. Ask the guy for the results of his last 5 AT tests.....

It will cost more to seek out and find upskilled design and construction professionals. But not to do so is false economy over the medium to long term.

Brave Harvey

Mick the Man, On the costs side, has he or his engineer done the sums of material/labour cost of internal slabbing vs wider cavity and good thermal bridging detailing?

It is my feeling that the professionals are not updated or just slugfesting it out to hold onto the old ways against the new advances in Part L. I am all for cost effectiveness but I am afraid that my brother will suffer due to a lack of foresight at this tricky time for construction.

Brave Harvey

Sinnerboy...Most engineers are not up to speed with wide cavity construction design in my own personal experience. So one finds a de facto / default max cavity of 150mm in a lot of cases

As regards the wide cavity construction, my brother was told that it is like building two separate walls, but I thought that you just double up on the wall ties, what are all the factors involving wide cavities?? Can you still use conventional blockwork cavity closers or do you need to invest in the proprietary insulated cavity closers.....

heavydawson

Brave Harvey wrote: »

As regards the wide cavity construction, my brother was told that it is like building two separate walls, but I thought that you just double up on the wall ties, what are all the factors involving wide cavities?? Can you still use conventional blockwork cavity closers or do you need to invest in the proprietary insulated cavity closers.....

The wall ties will need to be longer. Not sure if you need to add more of them per m2. That's a structural decision, and only the engineer can comment. If you've got a wide cavity, a blocklayer who builds the walls from inside may not be able to reach across the cavity from inside. This becomes more expensive if a two-storey, as you'll likely need scaffolding all around the outside of the house at the block-laying stage.
You'll also have to consider how the cills and windows will look. You already mentioned cavity closers, etc. It can and has been done, but for those wide cavities (225+mm), you need to do some homework.
I don't mean to knock it. I actually think a wide cavity is a good idea, and IMHO, the only time you should consider pumping beads in a new build.

fealeranger

heavydawson wrote: »

The wall ties will need to be longer. Not sure if you need to add more of them per m2. That's a structural decision, and only the engineer can comment. If you've got a wide cavity, a blocklayer who builds the walls from inside may not be able to reach across the cavity from inside. This becomes more expensive if a two-storey, as you'll likely need scaffolding all around the outside of the house at the block-laying stage.
You'll also have to consider how the cills and windows will look. You already mentioned cavity closers, etc. It can and has been done, but for those wide cavities (225+mm), you need to do some homework.
I don't mean to knock it. I actually think a wide cavity is a good idea, and IMHO, the only time you should consider pumping beads in a new build.

I built my house with a 300mm cavity. The wall ties do cost a little more at €1.30 each. You have to double them up around all openings like doors and windows which means a wall tie for every block. Closing the cavity should not be that big an issue. I am still not convinced with HRV systems but this is only my own opinion. I would agree with everybody here in saying definitly get a second engineer who is up to date with things.

fionn_mac

I was involved in a project (house) with 250mm cavity (filled with ecobead platnium), using teplo wall ties. you can use an insulated cavity closer e.g. kingspan kooltherm cavity closer (I'm not sure if this is your understanding of conventional) at the time they maxed 150mm but they can be coupled together, talk to one of the suppliers about it. what are the cill and door thresholds like - how does the door/window sit in the cavity?

If cost is the concern get a QS to compare the two options, and see if the wider cavity is much/any dearer, as opposed to something his engineer/builder is unfamiliar with and doesn't want to do.

you are giving your brother sound advice, echoed by other posters here. Maybe show your brother the thread - he does doesn't want to be in a position of regret in 3 years time. Its a steep learning curve with little chance of changing once he's on site so you'd want to make the correct decisions now.

heavydawson

fionn_mac wrote: »

I was involved in a project (house) with 250mm cavity (filled with ecobead platnium), using teplo wall ties. you can use an insulated cavity closer e.g. kingspan kooltherm cavity closer (I'm not sure if this is your understanding of conventional) at the time they maxed 150mm but they can be coupled together, talk to one of the suppliers about it. what are the cill and door thresholds like - how does the door/window sit in the cavity?

If cost is the concern get a QS to compare the two options, and see if the wider cavity is much/any dearer, as opposed to something his engineer/builder is unfamiliar with and doesn't want to do.

you are giving your brother sound advice, echoed by other posters here. Maybe show your brother the thread - he does doesn't want to be in a position of regret in 3 years time. Its a steep learning curve with little chance of changing once he's on site so you'd want to make the correct decisions now.

Definitely show your brother the thread!

Brave Harvey

=fionn_mac;83982445] what are the cill and door thresholds like - how does the door/window sit in the cavity?

Well in the windows case for the 250mm option, i'd imagine the cills sit on a steel angle support from the inside of the external block wall?

If cost is the concern get a QS to compare the two options, and see if the wider cavity is much/any dearer, as opposed to something his engineer/builder is unfamiliar with and doesn't want to do.

Yes it comes down to cost and the qs is loooked upon as an added cost.

sinnerboy

Brave Harvey wrote: »

Yes it comes down to cost and the qs is loooked upon as an added cost.

To make an omelette you must break some eggs.

heavydawson

Brave Harvey wrote: »

Well in the windows case for the 250mm option, i'd imagine the cills sit on a steel angle support from the inside of the external block wall?



Yes it comes down to cost and the qs is loooked upon as an added cost.

QS is a drop in the ocean compared to the overall cost of the build, and assuming this is someone who's never built before, having a qualified third party shed some light on where costs are coming from is recommended.
You can get a QS report for 500, and that is money well spent.

Brave Harvey

QS is a drop in the ocean compared to the overall cost of the build, and assuming this is someone who's never built before, having a qualified third party shed some light on where costs are coming from is recommended.
You can get a QS report for 500, and that is money well spent.

I myself believe that this would be beneficial. Really at planning stage, no. 1 decide on the plans, do a provisional ber, and then get a qs to do a price report. Then apply for planning. This to me would make most sense.