Please review my foundation/floor/wall junction detailing

[Hilldes]

Almost ready to submit this to Building Control. Any comments much appreciated...

Piling and ring beam will have separate detailed drawings.

 

[Mr Punter]

Cavity tray and weep holes.  Holding down details for sole plate.  What size is the block under the Marmox?  I would want something factory sized here, not cut with a bolster.

[tonyshouse]

For me the coldest place is on top of the dpc under the sole plate ? Just where you don’t want condensation to collect, I would add some mitigating insulation across the dpc 300 up, 300 below say 25mm eps 

 

perimeter insulation may as well be 100mm 

[Mr Punter]

Also, make the supporting block and Marmox 140mm so it supports the whole of the soleplate as it is currently straddling 3 materials which are unlikely to be completely level with each other.

[Hilldes]

1 hour ago, Mr Punter said:

Cavity tray and weep holes.  Holding down details for sole plate.  What size is the block under the Marmox?  I would want something factory sized here, not cut with a bolster.

 

Thanks @Mr Punter, will look at detailing cavity tray and weep holes - have not seen these in detailing for TF with render board external skin, but I guess water could enter the cavity and needs to go somewhere.

 

Sole plate fixing - will add these details when TF design completes. Interestingly, Marmox state that if the sole plate is "nailed" down then this can't go through the Termoblock. So the Thermoblock would need to go lower in the wall, and a 7N concrete block under the sole plate to take the "nail" - which I guess means the concrete block is colder and more risk of interstitial condensation at the sole plate DPC.

 

The non standard height blocks - I've not been comfortable with this either. Will look at using on standard height blocks at least for the inner skin.

[Hilldes]

1 hour ago, tonyshouse said:

For me the coldest place is on top of the dpc under the sole plate ? Just where you don’t want condensation to collect, I would add some mitigating insulation across the dpc 300 up, 300 below say 25mm eps 

 

perimeter insulation may as well be 100mm 

 

Thanks @tonyshouse, will look at EPS in the cavity. I guess no problem in filling the cavity so 50mm EPS. Can I actually bridge the DPC with EPS?

 

Perimeter insulation of 100mm sounds good given the wall make up - so this will be under the PIR wall insulation (the pink colour) and the service cavity.

[Hilldes]

1 hour ago, Mr Punter said:

Also, make the supporting block and Marmox 140mm so it supports the whole of the soleplate as it is currently straddling 3 materials which are unlikely to be completely level with each other.

 

Thanks @Mr Punter I'll check the Marmox data sheet. I vaguely recall it stating the Marmox block must not be wider than the blocks beneath it, but will check. Unless there are 140mm wide dense concrete blocks? 

[Mr Punter]

140mm wide blocks are widely available.

[tonyshouse]

Is ok to bridge dpc with eps, I would chamfer tomorrow edge to 45 and rub the breather membrane over it 

[Hilldes]

Could do with a bit more advice on this one please - relating to the structural concrete topping and UFH. These are constraints from the suppliers:

• The need to have 75mm concrete above the UFH pipes [Milbank installation instructions and BBA cert]
• The A142 mesh at half the depth of the concrete [Milbank installation instructions and BBA cert]
• The need to have the DPM above the EPS topsheet [Milbank installation instructions and BBA cert]
• UFH pipes as close to the EPS top sheet as possible, i.e. as low down in the slab as possible [Wunda]

So here are my options to meet some/all the above constraints:

1. Stick with A142 reinforcement and still cable tie UFH pipes to the top of the mesh. Downside: concrete topping will need to be circa 190mm deep to give 75mm cover above UFH pipes and have the A142 mesh positioned at mid height of the concrete topping. Downside 190mm deep concrete as opposed to 100mm.
2. Staple UFH pipes through DPM into the EPS top sheet. Downside: staples puncture the DPM. A142 mesh chairs need to avoid UFH pipes.
3. Staple UFH pipes through a thinner slip sheet into the EPS top sheet, moving the DPM below the EPS topsheet. Downside: DPM not in location specified on BBA cert. A142 mesh chairs need to avoid UFH pipes.
4. Mount UFH pipes in plastic pipe trays. Downside: A142 mesh chairs need to sit on plastic pipe trays.

Options 2, 3 and 4 could be simplified by using fibre reinforcement to concrete as opposed to A142 mesh. Tried to get quotes from Cemex and they don't do any of the fibre reinforcements in the Milbank BBA cert (see below).

 

Any thoughts please? @tonyshouse @Mr Punter

[Mr Punter]

What you had on the drawing looked fine.  Quite why you are looking at 190mm concrete I have no idea.  Polythene over the insulation.  75mm concrete with mesh 25mm from bottom would normally work.  Ties the pipes to the mesh.  How much is the floor costing?

[Moonshine]

A couple of comments from me

• use 140mm blocks on the inner skin to support the timber frame (as per @Mr Punter marmox blocks are available in 140mm.
• I have not seen the marmox block directly inline with the screed, i have only seem them designed inline with the floor insulation as below (https://www.bregroup.com/certifiedthermalproducts/product.jsp?id=3590&thermalId=908). Also are the marmox blocks designed to have sole plates screwed into them? i would check with marmox, also runs the risk of someone using too long a screw and bridging that nice expensive marmox block

• what is the u=value of the floor?
• I looked into these type of systems before and found they weren't cost efficient for a single house compared with a standard block and beam floor with PIR insulation in it.
• has your ring beam size been confirmed by a structural engineer? may be worth adding text such as 'please refer to structural design'
• 190mm concrete screed seems too much and i would have thought that 75-100mm would be fine. 

for your other detailing there is really good info here

 

https://www.bregroup.com/certifiedthermalproducts/selectcategory.jsp?st=2&pt=3&id=3590

[Hilldes]

10 hours ago, Mr Punter said:

 How much is the floor costing?

 

Thanks @Mr Punter Assuming you mean cost of the insulated B&B? Cost is similar to conventional beam and block. This thread covered the cost.

 

10 hours ago, Mr Punter said:

What you had on the drawing looked fine.  Quite why you are looking at 190mm concrete I have no idea.  Polythene over the insulation.  75mm concrete with mesh 25mm from bottom would normally work.

 

I'm not seriously considering 190mm concrete - just showing what I would need to do to meet the terms of the BBA spec and manufacturers installation instructions. 75mm concrete with mesh 25mm from bottom might normally work, but won't meet the terms of the BBA spec and installation instructions. 

 

I'm thinking if I don't strictly follow any of the conditions in the BBA cert it would be placement of the DPM below as opposed to above the EPS top sheet - as having DPM between the beams and the covering insulation layer appears fairly standard. This is my option 3 above.

[Hilldes]

Thanks @Moonshine.

 

140mm blocks are in the next version of the drawing.

 

You are right about fixings into the Marmox - will see how the timber frame supplier will fix the sole plate.

 

Thanks for the point on Marmox alignment with insulation as opposed to screed - I hadn't seen the diagram and will look into that.

 

Floor target U value is 0.13W/m2K, ideally 0.11W/m2K

 

Cost of the insulated B&B system - see above reply to Mr Punter with link to separate thread on cost of the insulated B&B versus conventional B&B. I was surprised how little price difference there was.

 

Ring beam - good point will add text to refer to the structural design.

 

Thanks for the BRE link - will spend a few hours there ?

[Moonshine]

39 minutes ago, Hilldes said:

Floor target U value is 0.13W/m2K, ideally 0.11W/m2K

 

When i looked at it i could get 0.12 W/m²K with a standard block and beam floor with 150mm PIR (0.022W/mK), this seemed to me to be more cost effective.

 

FLOORS

EXTERNAL BLOCK AND BEAM

OVERALL STRUCTURAL DEPTH tbc

U-VALUE 0.12 W/m²K

Floor deck: 75mm structural screed with embedded Under Floor Heating (UFH) piping

Insulation: 150mm rigid insulation boards (max thermal conductivity of 0.022W/mK).

Floor substructure: 150mm deep beams with 100mm blocks laid out to structural engineer specifications, over min 150mm ventilated floor void.

[Mr Punter]

@Hilldes can you post the BBA cert as I cannot find it?

 

You should have DPM / vapour barrier on the warm side (top) of the insulation.

[Hilldes]

2 hours ago, Mr Punter said:

@Hilldes can you post the BBA cert as I cannot find it?

 

You should have DPM / vapour barrier on the warm side (top) of the insulation.

 

@Mr Punter BBA cert attached. It's an add one as its logged in the name of the insulation manufacturer.

Warmfloor BBA certificate.pdf

Edited September 30, 2020 by Hilldes

[Hilldes]

2 hours ago, Moonshine said:

 

When i looked at it i could get 0.12 W/m²K with a standard block and beam floor with 150mm PIR (0.022W/mK), this seemed to me to be more cost effective.

 

@Moonshine That is why I was asking in the other post if I was missing something on the costs. Travis Perkins un-discounted cost for just the beams + 7N concrete infill blocks is little different in price to the Milbank system -which includes the EPS top sheet - so no need to buy PIR. And little difference in overall depth as yours. Still wondering if I'm missing something.

Edited September 30, 2020 by Hilldes

[Mr Punter]

 Looking at the BBA cert it may be best to clip the mesh to the insulation through the vapour barrier and have the mesh above centrally.  

[Hilldes]

1 hour ago, Mr Punter said:

 Looking at the BBA cert it may be best to clip the mesh to the insulation through the vapour barrier and have the mesh above centrally.  

Thanks @Mr Punter agree that will meet the spec in the BBA cert. Only downside is that if I clip the pipes to the insulation that will puncture the DPM - from other threads on here most appeared to say that was not advisable but one view (might have been nickfromwales) was that it is relatively common for ufh pipe clips to puncture the DPM and they essentially sealed the hole they made.

[Carrerahill]

On 13/09/2020 at 18:28, Hilldes said:

 

Thanks @tonyshouse, will look at EPS in the cavity. I guess no problem in filling the cavity so 50mm EPS. Can I actually bridge the DPC with EPS?

 

Perimeter insulation of 100mm sounds good given the wall make up - so this will be under the PIR wall insulation (the pink colour) and the service cavity.

Don't fill the cavity, always maintain a gap.

 

If you fill with EPS if water were to gather on top of the EPS nothing to stop it running inwards, no gap also means moisture could be trapped.

[Mr Punter]

17 minutes ago, Hilldes said:

Thanks @Mr Punter agree that will meet the spec in the BBA cert. Only downside is that if I clip the pipes to the insulation that will puncture the DPM - from other threads on here most appeared to say that was not advisable but one view (might have been nickfromwales) was that it is relatively common for ufh pipe clips to puncture the DPM and they essentially sealed the hole they made.

 

The membrane is only there to stop concrete escaping between the board joints bridging the insulation.  A few holes will make no difference.  You could just tape all the joins.

[Hilldes]

2 hours ago, Mr Punter said:

 

The membrane is only there to stop concrete escaping between the board joints bridging the insulation.  A few holes will make no difference.  You could just tape all the joins.

 

Thanks so much for your help @Mr Punter From my basic knowledge of floor build up (all gleaned from this site by the way ?)...Thin polyethylene "slip"? sheet over EPS topsheet - to stop concrete flowing through joins in insulation and no issue if this is punctured by the UFH clips.

 

This would assume the DPM (e.g. 1200 gauge Visqueen) would be below the EPS top sheet. The BBA cert says DPM should be above the top sheet. I think you said that too? Too many membranes ?

[Hilldes]

2 hours ago, Carrerahill said:

Don't fill the cavity, always maintain a gap. If you fill with EPS if water were to gather on top of the EPS nothing to stop it running inwards, no gap also means moisture could be trapped.

 

Thanks @Carrerahill how about 25mm EPS filing half the 50mm cavity, or no insulation?

[Mr Punter]

You don't need the DPM.