Generally - Wall/Slab/Roof build-up advice for very large new build.

[ElliotP]

2 hours ago, MR10 said:

 

I'm assuming 'worked with before' was on a much smaller scale and detailing than required for this proposed build.

Thread carefully.

2 hours ago, saveasteading said:

 

Beware. Do you mind losing a friend?  Some things will go wrong. As long as you pay extra every time it is requested ( and happily so) then it could be OK.

 

Indeed, it was a 2 story extension, sizeable but not on the scale of this.  However he's experienced, smart and enthusiastic.  We dealt with plenty of curve balls together hidden sewers, build over agreement, deep footings etc.  We got through it. We're not that close anyway 😁

 

2 hours ago, gavztheouch said:

Good luck! Im builidng a 210m2 shell for hopefully a similar budget of 300k. It should be doable depeding on how much work you do yourself.

 

Edit, I just reread your post and noticed you have a swimming pool triple garage and annex are these all inlcuded in your 300k budget. Minus the swimming pool I would budget around £600k to build the weather tight shell.

 

That's interesting, and also slightly unnerving. When I say swimming pool - in the '£300k' (which admittedly i've pulled out of my ass), I'm nut budgeting the actual pool in that or even the hole in the ground - just the room to house it, which will be on the bottom of the 3 floors. So I'm hoping that given we're doing 3 stories will help.  The garage and annexe will be combined, with the bedrooms above the garage, again looking at savings there.  No idea on my m2 yet until I get some plans, but looking at yours, that's about £1400 / sqm just for the shell?  Is this 2 stories?  Ex VAT also assuming it's a new build? 

We'll need to get the plans and discuss with the builder before I have any idea where I am, there are certainly going to be tradeoffs.  

 

41 minutes ago, joe90 said:

Parse coat, cement render (even between floors) and plaster finish. Around windows and reveals was air proof foam and foaming glue (not a big fan of taped membranes).

The reveal deal is also what I was concerned about, especially on a wide cavity. I had a quick research.  Suggestion looks to be boarded with ply, and foamed for airtightness, and some more detailing I'm yet to understand.

 

2 hours ago, joe90 said:

I built brick and block with 200mm cavity, wall ties were not that expensive, I also used concrete lintels internally and brick arches externally so no cold bridging. You will read many threads here where attention to detail makes a big difference especially with airtightness (don’t let trades bore random holes in your membrane whatever it is).

What kind of ties did you use? Are basalt a requirement due to the bridging or is it not worth it? 

 

So overall judging by the responses here, there hasn't been a suggestion of going timber frame which I expected to be honest. So this has kind of validated my traditional wall build up a little more, even at a wider cavity.  I just need to nail down the slab, roof and junctions. 

[Adsibob]

11 hours ago, jack said:

But in general, GSHP setups are at least double to price of an ASHP of the same output. If properly done (and that isn't always the case), the GSHP will have slightly higher efficiency, but not enough to ever pay back the price difference.

GSHP does have a significant aesthetic and comfort advantage though: much of the ugly stuff is underground and there is less noise. Might not be an issue on a large plot where you can hide it away in the corder somewhere, but it’s a problem in densely populated areas with small plots.

[joe90]

57 minutes ago, ElliotP said:

What kind of ties did you use? Are basalt a requirement due to the bridging or is it not worth it? 

I decided the cold bridge from stainless ties was minimal (not everyone agrees) so I used them as basalt are so expensive  for (what I decided) was little return. 
 

 

59 minutes ago, ElliotP said:

need to nail down the slab,

I used strip foundations and copied this (nearly, we moved the DPC one block lower on the internal wall so as not to create a slip plane above the skirting board then added a second DPC in the outer wall above ground level, the whole house was surrounded in a French drain as the water table was high.

 

[Iceverge]

3 hours ago, joe90 said:

decided the cold bridge from stainless ties was minimal (not everyone agrees) so I used them as basalt are so expensive  for (what I decided) was little return. 

I calculated this. From memory all you need to do is widen the cavity by about 5mm to make up the difference. SS every time.

 

Here's my alternate version of the above detail. 

 

1. Full fill of EPS beads, right to the foundation. Allowance for mortar droppings so they won't build up to DPM level. 

2. Less thermal blocks, they don't really make a difference to the heat loss below the insulation in the floor. 

3. 2 x Layers of EPS 150mm insulation with the DPM in between for protection. 

4. Separate DPC on outer leaf. 

5. 50mm insulation at perimeter really helps the heat loss. 

6. Much easier to level this concrete floor than the other design. 

7. Allows for the use of cavity ties below the DPC increasing stability.

8. Simpler threshold detail for DPM. 

[ElliotP]

Thank you both @joe90 / @Iceverge, that's really helpful and exactly what I needed - some real world validation on the diagrams I've been staring at. 

[jack]

13 hours ago, Adsibob said:

GSHP does have a significant aesthetic and comfort advantage though: much of the ugly stuff is underground and there is less noise. Might not be an issue on a large plot where you can hide it away in the corder somewhere, but it’s a problem in densely populated areas with small plots.

 

Aesthetic, agreed. If you don't have an out-of-sight place for one, they are generally pretty ugly. We're lucky that we were able to site ours on the far side of our attached garage, where it's out of sight unless you walk along that route (and there's generally little reason to do so).

 

I'm less sure about comfort. There are lots of reports about how noisy GSHP pumps are, to the point where it's sometimes recommended they be sited in their own sound-insulated housing outside the main building envelope.

 

I can't hear my ASHP when it's running unless it's a very still day and I stand pretty close to the unit.

 

I'm not saying there are no use cases for GSHP, just that the economics rarely make sense if you can choose between one or the other (as appears to be the case with OP, since he mentioned both).

[ElliotP]

Hi all, 

 

Back with a small update on this and looking for some validation if you don't mind.  I've just started off with my architect and have advised on which way i want to go with the wall (200mm, eps pumped in).  He's fired back some questions/advice (he's a good man and making sure), i just wondered if you could pick your brains, I think i've got it covered but just want to be sure.

Lintels - he's advised that he can't find off the shelf thermally decoupled lintels for a 200mm cavity.    To me this is an easy one - we're using two separate standard lintels, EPS goes between as with the rest of the cavity - it doesn't get better than that does it?

Secondly he's advised that a 150mm cavity with Celotex 140mm Cavity Wall 21 would be thermally better than EPS.  I've advised that while that's true, the benefits of EPS outweighs the thermal characteristics, that being, more guarantee of a full-fill, not having to rely on builders trying to install it (probably poorly), such as leaving gaps and holes, going around wall ties etc. As well as (i'm assuming) it's a hell of a lot cheaper than PIR.  To me it seems like a perfect solution of let the brickies brick, and let the insulators insulate. Everyone knows what their doing and can (hopefully) do it well.

Thanks as always! 

[Trw144]

On 20/03/2024 at 01:28, Iceverge said:

I calculated this. From memory all you need to do is widen the cavity by about 5mm to make up the difference. SS every time.

 

Here's my alternate version of the above detail. 

 

1. Full fill of EPS beads, right to the foundation. Allowance for mortar droppings so they won't build up to DPM level. 

2. Less thermal blocks, they don't really make a difference to the heat loss below the insulation in the floor. 

3. 2 x Layers of EPS 150mm insulation with the DPM in between for protection. 

4. Separate DPC on outer leaf. 

5. 50mm insulation at perimeter really helps the heat loss. 

6. Much easier to level this concrete floor than the other design. 

7. Allows for the use of cavity ties below the DPC increasing stability.

8. Simpler threshold detail for DPM. 

 

What U value does this come out at? Ditto for yours @joe90

[saveasteading]

1 hour ago, ElliotP said:

the benefits of EPS outweighs the thermal characteristics

 

I don't know why I am suspicious of blown eps, but I just haven't ever come across it.

Maybe that's a good sign that it isn't known for problems.

I think of it as a retrofit in old council flats, perhaps unfairly.

 

What stops dampness from creeping across ball to ball?

 

My cavity insulation of choice is cavity mineral wool batts. There is no chance of water crossing through, and it is idiot proof  (No, it is idiot resistant).

Also it fills the cavity and prevents brickies from dropping mortar into the cavity or parking drink cans and fag packets therein. The labour element of fitting it is tiny.

Insulation level is much the same as eps I think, without checking.

[Iceverge]

5 minutes ago, Trw144 said:

 

What U value does this come out at? Ditto for yours @joe90

 

Our 250mm cavity is 0.13ish. Don't get carried away with teplo ties or lightweight inner blocks. Much cheaper and easier to just increase the cavity width by a few mm. 

 

6 minutes ago, saveasteading said:

What stops dampness from creeping across ball to ball?

 

 

Magic. 

 

Also I don't know. 

 

Some possibly theories. 

 

1. The matrix is too dense to allow wind to blow the water through them.

2. The temperature gradient across the insulation encourages the water to go out rather than in. 

3. The surface of the beads is too hydrophobic. 

4. The outer side of the internal leaf is at room temperature and so is warm enough to evaporate the tiny amount of water that does make its way in there. 

5. Assuming any water entering the cavity originates from the outer leaf the matrix of beads at worse can split half the water to go inwards or half to go outwards at any layer. If you keep halfing any drip from a layer of beads above and sending half inwards and half outwards only a tiny harmless amount makes to the inner leaf. 

6. The matrix of beads is actually very open and most of the water flows straight down to the foundation or to a cavity tray. 

 

18 minutes ago, saveasteading said:

and it is idiot proof  (No, it is idiot resistant).

 

Nothing is idiot proof.

 

You might outsmart them today and tomorrow and  even the day after. 

 

However they'll be there, waiting in the long grass, ready to out-stupid you for the rest of time. They are remarkably persistent. 

 

[saveasteading]

5 minutes ago, Iceverge said:

matrix of beads is actually very open

1/3 air if the balls remain spherical and touching infinitesimally.

 

I like and accept your thoughts. I am inclined to believe it works for one or more of these reasons.

 

6 minutes ago, Iceverge said:

Nothing is idiot proof.

I thought I had them beaten when 2 part epoxy started to come with the special mixing nozzle. No chance of poor mixing or even forgetting to add part 2.

NO. Push the bolt in without turning and it nearly all comes flying out again.

I'll be remembering other examples as the day proceeds.

[SteamyTea]

1 hour ago, saveasteading said:

What stops dampness from creeping across ball to ball

The larger surface area.

4πr²

 

A cylinder has a surface area that is.

2πrh+2πr²

 

Mineral wools can be modelled as cylinders.

[joe90]

1 hour ago, Trw144 said:

Ditto for yours @joe90

I didn’t do any calculations mine was based on gut feeling, all I know was my bills were small and I was very comfy.

[Mike]

On 19/03/2024 at 21:43, Adsibob said:

GSHP does have a significant aesthetic and comfort advantage though: much of the ugly stuff is underground and there is less noise. Might not be an issue on a large plot where you can hide it away in the corder somewhere, but it’s a problem in densely populated areas with small plots.

It doesn't necessarily have to be outside - I've seen it I've seen it installed inside in a narrow central London infill house, with boreholes going down through the floor.

[saveasteading]

54 minutes ago, SteamyTea said:

Mineral wools can be modelled as cylinders.

Water doesn't get past the surface on cavity batts. 

 

55 minutes ago, SteamyTea said:

The larger surface area.

4πr²

But time is infinite, so it will continue to spread.

 

4 minutes ago, Mike said:

boreholes going down through the floor.

I've seen this too, but they didn't work and are now ss by ashp. Refurbing an 80m borehole if it ever needs it could be tricky in the cupboard under the stair.

[SteamyTea]

11 minutes ago, saveasteading said:

1 hour ago, SteamyTea said:

Mineral wools can be modelled as cylinders.

Water doesn't get past the surface on cavity batts. 

That is because of the length.  If the cavity was a few millimetres, then it would.  But that same is true of just about any material.

12 minutes ago, saveasteading said:

But time is infinite, so it will continue to spread.

At any temperature above absolute zero (0K) evaporation of any material can take place (and sublimation).  It is the way materials work.

So it is not really time, per sec, that is the governing factor, more temperature, on the kelvin scale.

It is how heat pumps work, and what governs their efficiency (Carnot Cycle).

Prof (Dr) Richard Feynman was the bloke that formulised all this back in the late 1940's, building on Maxwell's Demons.

Better than that though, it is all statistics.

 

But basically, if there is a long enough path, then liquids will not move past a set limit.  They get too thin and start to evaporate.  A sphere has the best surface area for a path length, and plenty of space for another gas between the balls.