Wall design

Minty1212

Hello there,

I am looking for advice about my proposed new build. I am very early into the project.
I have chosen a architect who is proposing this type of wall construction.
Can you please give me an opinion on the pros and cons.
He does not like the idea of external insulation after his experience of it in the US.
If there is any more info that you need please ask.
Many thanks in advance
Minty

heinbloed

Contact a civil engineer, ask him/her to use wufi. And demand a long-term indemnity insurance.

Paterson

In my opinion your loosing out on being able use the thermal mas of the concrete wall also with insulation internally the elimination of thermal bridging can be tricky, hope that helps

Minty1212

Hi Paterson

At what point would the thermal bridging occur?

Hi heinbloed

The architect will be submitting his design to Homebond for approval.

This design is done so that a lot of the work can be done by less qualified people like my self and can be done in stages eg Concrete Blocks then internal works as and when finances are available.

The whole project has a very tight budget 1500sq ft 60 to 80k finished.

The time this will take could be up to 3 years due to finances.

Thanks again

Minty

Paterson

well if you use a concrete floor there could be a possibility of one where floor slab goes through insulation not saying they cant be eliminated just attention to detail and site supervision will be key

sas

Minty1212 wrote: »

Hello there,

I am looking for advice about my proposed new build. I am very early into the project.
I have chosen a architect who is proposing this type of wall construction.
Can you please give me an opinion on the pros and cons.
He does not like the idea of external insulation after his experience of it in the US.
If there is any more info that you need please ask.
Many thanks in advance
Minty

Couple of questions.

1. Is this a timberframe structure?

If it is I'd be concerned. First off your budget is tight, very tight. So you'll be looking for a very competitive timber frame structure. There is an awful lot of crap being turned out by TF companies. A good frame will cost money which your budget may not have space for. Don't get mislead by ITFMA membership or NSAI certification. There are plenty of TF companies with\in both and their work is still shocking.

You're talking about building over 3 years. Does your architect think it's a good idea for that TF to be left at various stages of completion for that period? If you have the money to complete the roof, install the windows and complete the outerleaf within a couple of months of the TF being erected (at most) then this may be less of an issue. There are those that believe a TF shouldn't be allowed to get wet at all however.

I should underline that if it's not TF, the build up makes no sense whatsoever in my opinion. I can't even tell how it would be built on site.

2. Why block on the flat for the outer leaf?

I've never seen this done for an outerleaf. It makes absolutely no sense whatosever when you're on a tight budget.

Also, you mention it will be going forward for Homebond approval. I wasn't aware that homebond do approvals, they are an insurance company. You are talking about doing alot of the work yourself. Homebond only cover houses built by specific contractors. Something sounds a little "off" with this.

I will defer to the actual construction professionals here but imho something sounds very strange about the direction you are being encouraged to go.

If I've gotten the wrong end of the stick here then please post more details.

Minty1212

Hello sas.
The house is not timber frame.
The architect says that the outer shell consisting of the blocks and roof can be finished first,then the windows, then I can start on the interior in stages.
He has 22 years of experience in design but mostly large commercial developments in Ireland, US and the Middle East.
The design is radical as he has explained it and there elements that he is still working on.
He has said that it is very important to him that this design works for me and my circumstances due to my financial circumstances.
He has said that this design will archive Passive House Standards.
He has done a course in Passive House Design.
He is a full member of the RIAI and has all the paperwork re insurance.
But I will talk to him about all your concerns
If there are any further points that you or others can think of please let me know.
Many thanks again
Minty

BryanF

Minty1212 wrote: »

Hello sas.
The house is not timber frame.
The architect says that the outer shell consisting of the blocks and roof can be finished first,then the windows, then I can start on the interior in stages.
He has 22 years of experience in design but mostly large commercial developments in Ireland, US and the Middle East.
The design is radical as he has explained it and there elements that he is still working on.
He has said that it is very important to him that this design works for me and my circumstances due to my financial circumstances.
He has said that this design will archive Passive House Standards.
He has done a course in Passive House Design.
He is a full member of the RIAI and has all the paperwork re insurance.
But I will talk to him about all your concerns
If there are any further points that you or others can think of please let me know.
Many thanks again
Minty

Minty, If money's tight,

1. why be a guineapig for a new wall system? 'still working out' elements of his 'radical' design...
2. how long does homebond procedures take?
3. how much does calcs of thermal bridge detailing cost?
4. and how much contractor head scratching at non-standard details cost you?

Although, i share you archs reservation of using EWI in a new builds, and his passion for revolutionary building methods, your proposal seems overly complicated.

BUT maybe this is a response to your brief of a dry shell to wok within over an long time frame?

That said we really need to understand how the windows, floor and eaves work, along with where exactly the air-tightness membrane will be installed at these junctions.

heinbloed

One problem I see with natural fibres in the cavity is moisture ingress. These fibres can sagg and can serve as food for moulds and insects. Against consumption they're usually treated with a salt, Boro, this will seep out into the place of lowest concentration if allowed. And this would be the wall, be it the external or internal wall.
The (technical foam-) boards are covetred with aluminia foil, this would rot/oxidise very quickly when in contact with salt.

Salt in a cavity wall is doomed to leak, to react. The cavity wall is build for a reason, namely to keep away moisture from the interior wall.
The straps/wires holding the walls together aren't designed for salty environs as well. Maybe stainless steel ones are....

Are you sure your architect/civil engineer has enough knowledge about the basics of material choices? No insult, but the salt issue/moisture interaction in the shown design seems very problematic.

There are rules about how much salt is allowed in concrete (-blocs), the max. content.

At contact with loadbearing reinforced concrete (lintels, ring beam, ring anchor) this issue would occure as well, the concrete coverage of the steel would have to be at least 10 mm more than standard/necessary for loadbearing issues.To protect the steel against corrosion.
What means less space for insulation, more risk of condensation....

Contact a civil engineer to give his opinion, as the previous poster said already: with such a design you're a guinea pig. The civil engineer would be your life insurance in this case.

Have you thought about cladded EWIS or monolithic block walls ? Timber frame?

sas

Minty1212 wrote: »

Hello sas.
The house is not timber frame.
The architect says that the outer shell consisting of the blocks and roof can be finished first,then the windows, then I can start on the interior in stages.
He has 22 years of experience in design but mostly large commercial developments in Ireland, US and the Middle East.
The design is radical as he has explained it and there elements that he is still working on.
He has said that it is very important to him that this design works for me and my circumstances due to my financial circumstances.
He has said that this design will archive Passive House Standards.
He has done a course in Passive House Design.
He is a full member of the RIAI and has all the paperwork re insurance.
But I will talk to him about all your concerns
If there are any further points that you or others can think of please let me know.
Many thanks again
Minty

Hi Minty,

Ok, if it's not timber frame I assume something is missing from your diagram.

What is the airtight membrane attached to?
What is keeping the insulation in place because as it stands in that sketch there is a board "floating" on one side and an airtightness membrane "floating" on the other side.

Airtight membranes are not required to be used on masonry walls, even in PHs. My own home is being designed by the PHI themselves with the aim of obtaining PH certification. My airtight layer is the plasterwork on my block work. We don't have a service cavity, that's typically a timber frame detail.

Airtight membranes and tapes get pretty expensive over a build. Again, I'd be concerned for you on your budget constraints.

Any updates for that sketch?

sas

heinbloed wrote: »

Have you thought about cladded EWIS

Can you post a link to an example of this? It's not something I've come across and I'm curious about this.

slowburner

Minty1212 wrote: »

Hello there,

I am looking for advice about my proposed new build. I am very early into the project.
I have chosen a architect who is proposing this type of wall construction.
Can you please give me an opinion on the pros and cons.
He does not like the idea of external insulation after his experience of it in the US.
If there is any more info that you need please ask.
Many thanks in advance
Minty

The house I live in was built in a similar way in the '80's by a Canadian. There have been no problems whatsoever.
I don't see any membrane on the interior of the blockwork? I'd be concerned about that.

sas

slowburner wrote: »

I don't see any membrane on the interior of the blockwork? I'd be concerned about that.

Membranes are never used on the interior face of the outer leaf when a ventilated cavity is present. What's your concern?

slowburner

Condensation on the insulation?

sas

slowburner wrote: »

Condensation on the insulation?

Afaik condensation (should it occur) will come warm air escaping into the cavity from inside, not cold air hitting the insulation from the outside.

To be honest, the build up as sketched is clearly missing something. If it's a block inner leaf then there's a few obvious problems.

If it's not a block inner leaf then it has to be a timber structure that is planned on being build after the block leaf is up.

Bottomline, right now the membrane, boards and insulation are floating. They have to be supported by some structure.

slowburner

sas wrote: »

Afaik condensation (should it occur) will come warm air escaping into the cavity from inside, not cold air hitting the insulation from the outside.

To be honest, the build up as sketched is clearly missing something. If it's a block inner leaf then there's a few obvious problems.

If it's not a block inner leaf then it has to be a timber structure that is planned on being build after the block leaf is up.

Bottomline, right now the membrane, boards and insulation are floating. They have to be supported by some structure.

You don't need heated air from the interior and cold air from the exterior to get condensation. Think of a frosty night followed by a warm morning. The variability of weather in this island is well capable of causing the conditions for condensation in the space of minutes.
Agree with you on all the rest, though.

heinbloed

Sas asks:

Have you thought about cladded EWIS
Can you post a link to an example of this? It's not something I've come across and I'm curious about this.

Here a company serving the upper market:

http://www.schueco.com/web/uk

Click onto 'fascades'.

There are many more system providers.

Cladding can be done with many materials and methods. Check the possibillities to clad with ST/PV panels, these are wind-and weather proof and have an ongoing benefit. And are relative cheap per m2, at least when taking subsidies into account. They might pay for themself in the long term.They can be made to meassure, fake panels can be used in a solar cladding application to fill gaps when using standard sizes. This results in an even optical impression, the architect's preference.

sas

slowburner wrote: »

You don't need heated air from the interior and cold air from the exterior to get condensation. Think of a frosty night followed by a warm morning. The variability of weather in this island is well capable of causing the conditions for condensation in the space of minutes.
Agree with you on all the rest, though.

Fair point, I'd missed that scenario.

I assume you'd want the membrane on the outerface of the "board" and not on the inner face of blockwork.

I had pretty much decided this was the case anyway because I really think that this is a TF in everything but name.

Hopefully, minty will be by soon enough.

slowburner

sas wrote: »

I assume you'd want the membrane on the outerface of the "board" and not on the inner face of blockwork.

I'm sure you're right that it's standard practice not to have a membrane directly on the blockwork but can you tell me what the reason is, would it cause efflorescence or something like that?
I'm curious because I'm pretty sure there's a membrane directly in contact with the blockwork in my own place. There haven't been any problems except last winter, there was a deep coating of ice crystals on the exterior. I put up a post in the weather forum and it was suggested that it was the product of freezing fog - I wasn't so sure.

fclauson

heinbloed wrote: »

.... Check the possibillities to clad with ST/PV panels, these are wind-and weather proof and have an ongoing benefit. And are relative cheap per m2, at least when taking subsidies into account. ..........

No subsidies or grants on new builds for this type of technology

sas

slowburner wrote: »

I'm sure you're right that it's standard practice not to have a membrane directly on the blockwork but can you tell me what the reason is, would it cause efflorescence or something like that?
I'm curious because I'm pretty sure there's a membrane directly in contact with the blockwork in my own place. There haven't been any problems except last winter, there was a deep coating of ice crystals on the exterior. I put up a post in the weather forum and it was suggested that it was the product of freezing fog - I wasn't so sure.

I can offer my opinion only. This is based on the assumption that unless the membrane is perfectly sealed (in practical terms) it's pointless.

For TF the frame goes up first. The membrane is installed as part of this, it's basically stapled to the frame. It can be taped easily and fully sealed. The outer block leaf is tied to the TF using straps that are screwed through the membrane into the timber. The fact that the that straps are screwed in helps to counter balance the fact that the membrane has been breached i.e. metal strap is tightly fitted over the hole made by the screw.

For our traditional masonry we don't use membranes. I assume it's primarily because we don't need them. Traditional build almost exclusively uses plastic based insulants. These won't be affected by the few mornings a year where the circumstances you described (frosty night, warm day) arise and you get condensation on the outer surface of the insulation.

I also can't imagine how you'd install a membrane between 2 leafs as they both rise together.

Make sense?

slowburner

Yep.

harry21

sas wrote: »

Hi Minty,

What is the airtight membrane attached to?
What is keeping the insulation in place

Have we an answer to this? Surely for such a system there must be some stud work to attach the barrier and plasterboard to.

I also don't think that much point to the block on flat andd in summary I don't think it would be my choice of external wall.

AMG86

Going back to Homebond. They will not be in a hurry to pay out in the event of a claim. Better to ensure that the build is right from day 1.

Radiotower

I'd imagine that it is going to be timber frame on the inside of the blockwork but he's not calling it timber frame because the block on the flat is the supporting structure for the roof, so it really just a timber stud.

sas

Radiotower wrote: »

I'd imagine that it is going to be timber frame on the inside of the blockwork but he's not calling it timber frame because the block on the flat is the supporting structure for the roof, so it really just a timber stud.

Yeah, that's what I'd decided but really wanted Minty to respond. As the structural wall is a solid wall the detailing at the foundation for the floor wall junction will need to allow for this i.e. make sure the cavity created between this stud and the block can extend below the finished floor level.

A wide cavity would easily meet Mintys needs and budget. There isn't a chance in hell that this is doable on site anyway. As the stud needs to be built in situ you couldn't put the membrane wrap onto it in a continuous manner like a typical TF.

Something else that just struck me. If the house has structural internal walls, they couldn't be constructed using block work because in order to tie them into the structural outerleaf, the cavity would need to be breached.

This is complete insanity if what we're assuming is true...

I really hope Minty comes back to update us.

Minty1212

Dear All,

I must firstly apologize for not responding earlier. This was because I have been back to the UK to earn some much needed funds for the build!!.

The house build at the moment has come to halt due to information that we are waiting for from the Land Registry re a possible Right of Way that could be on my land.

What I have just done is printed off all your concerns with the wall design and will be giving them to my architect for a reply.

As soon as he does I will post it on this thread.

Once again many thanks to all that have commented.

Minty:)

sydthebeat

minty, what a strange construction!!

i would have a few issues.

1. if the structural element is teh external 215 blockwork, then all internal floors, walls etc have to support on it. This leads to a myriad of thermal bridging through your insulation layer to such a degree, it would be my opinion that the thermal bridging factor would be about 0.3-0.5 in this dewlling. This means that about 66% of all the heat lost in this dwelling would be through these thermal bridges alone, and only 33% through the usual heat loss elements. Thats an awful lot of insulation negated through thermal bridges.

2. The condensation point wil occur somewhere near the blockwork and the insulation. assuming your installing timber floors, this puts the condensation point at the worst possible position .. right at structural points where timbers are supported!! god help you if your proposing concrete floors!! the thermal bridging would be much worse!

3. compliance with building regulations. current building regulations require a thermal bridging factor of 0.08. Your architect will have to detail out ever single junction, calculate the thermal bridging factor using software such as therm 5.0, and then calculate the whole house value. This work is very time consuming and could take a person a whole week to do for a domestic dwelling. Is he covering this work? Also, will he do the wufi calcuations to prove that interstitial condensation is not going to be and issue where and how the insulation is held??? wet cellulous will sag.. sheeps wool is very expensive. If he is proposing breathable insulations, what internal boarding is he proposing, and how does he intend to vapour check this?

4. costs. as another poster has said above, if money is tight the last thing you want to do i send up being the guinea pig for a construction system.

5 passive levels... sorry, but not a chance in hell will this method meet passive thermal bridging levels without HUGE cost to you. The vast maority, if not all, of passive level houses have the superstructure in the internal... think EWI, timber frame.. even cavity wall. Putting the super structure to the external just simply does not make sense. I think he will come to that conclusion with more investigation.

6. DPC's. Where a cavity is created, dpcs need to be introduced to ensure that moisture which enters the cavity, either by condensate, or weather driven, is allowed to drain to teh external. How does he intend to introduce dpc at jambs, over heads, in all the standard areas, if theres no initial frame internally to work off before the blockwork?? Also, how will this internal frame work stand without connection to the external blckwork... and if there is to be connection to the external blockwork, how is the cavity vented.


To be honest, i admire the pushing of the envelope... but i feel the architect has come up with some amalgamation of TF, cavity wall, and dry lining... and not improved on any of these existing systems....