How to determine finished floor height using beam and block?

[ruggers]

I have some house plans approved for a masonry build which now need to switch from slab floor construction to beam and block which I've never used before.

 

I'm having trouble understanding how you align the inner and outer leaf brick courses so that the inside finished floor height is level with the cavity wall DPC that the external doors will sit on. If I add a 225mm inner leaf block on top of the beams & then use 150mm floor insulation on top of the beams + 50/60mm screed, it works out well at 210mm, which is under the 225mm block DPC level and leaves some room for tiled floor surface before the low door threshold. This makeup = 0.12W/m2k
 

My SAP has specified 0.10W/m2k using 150mm PIR which you can't achieve, it would require 190mm insulation which throws the heights out a lot.

190mm insulation + 50/60mm of liquid screed = 250mm or 270mm with a tile. This sits higher than a block but 30-50mm too low for a block and a brick to match DPC.

 

How do you make up the floor levels to match low level door threshold/DPC, is it a case of you have to add more insulation and more screed to get to 300mm DPC? With a slab floor you can offset the height of the slab to suit so I could have any thickness of insulation.

 

Is 0.10 vs 0.12 W/m2K a massive difference in a heat loss calculation or noticeable in the real world?

 

I planned on having 150mm two brick courses step down to my outside finished floor level with the exception of the front door which is a ramped access low threshold to comply with regs.

 

From the top down, my floor make up is,

Minimum 50mm liquid screed containing wet underfloor heating (May need to be 60mm in some places to account for 10mm curve on beams)

150 or 190mm PIR insulation. 

150mm concrete T beams with 100mm block infill and 50mm slip bricks.
 

[PeterW]

2 minutes ago, ruggers said:

Is 0.10 vs 0.12 W/m2K a massive difference in a heat loss calculation or noticeable in the real world?

Nope..

 

Why not consider using one of the insulated beam systems and then make your slab 100mm flowing concrete with the UFH inside it and that’s a finished surface to work from ..??

Jetfloor is one, think Tetris is another ..?

 

[ruggers]

With standard beams 150 insulation seems less of a head ache then. increasing insulation to 190 or more and more screed, plus another house course of bricks is £1000's.

 

I'll have a look into them thanks, have heard the names some time ago but thought some insulation must still have to run over the top of beams and block as the beams otherwise the prestressed concrete would have a lot of cold bridging? Going from slab floor to beams requires 10mm more PIR ecotherm told me.

 

I liked the idea of a thinner screed vs thicker for reaction times although with weather compensation it's probably less of an issue.

 

 

[crispy_wafer]

Similar floor buildup as what I've got in progress.

 

Block and beam, 150mm of PIR, 60mm screed at the front door threshold - which is 15mm from memory.  I just went with what the door manufacturer recommended, in reality I should have waited and perhaps specified a slighty larger threshold.

 

When measured from the top of PIR to bottom of the door I have about 85mm so I've got a good 25mm for flooring depending on how flush I want the flooring to be.  I've settled on recessing a mat at the door opening, and glue down bamboo flooring @ 14/15mm so should work out ok.  Depending on thickness of mat I will grind out 5-10mm from the screed.

[saveasteading]

You are allowed to trade off insulation in the floor against the walls and roof.

Not the best idea if you have UFH*, but worth thinking about if the depth us critical.

* esp when the floor has cold air under it.

[Canski]

If you look at litecast website there are several examples of beams with insulation infill maybe one of those will be for you.  Without seeing photos / plans I’m confused as to what the issue is. 

[Temp]

4 hours ago, ruggers said:

I'm having trouble understanding how you align the inner and outer leaf brick courses so that the inside finished floor height is level with the cavity wall DPC that the external doors will sit on.  

 

Not sure I quite follow the problem but most level access Part M doors are done something like this...  There is a concrete sill and the DPM/C is under that at the door. The DPC in the external leaf is higher.  The DPC can be higher than 150mm above ground level.

 

 

 

 

 

Edited October 25, 2022 by Temp

[ruggers]

4 hours ago, saveasteading said:

You are allowed to trade off insulation in the floor against the walls and roof.

I didn't realise it was a whole house calculation. I mean SAP has specified 150mm as 0.10w/m2k, so i could do this and hopefully pass. I only know its incorrect because i was made a few enquiries and some of the insulation suppliers calculated my wall and floor make up for their products and all said i need 180 to 190mm. if i fit 150mm its 0.12w/m2k. Part of my existing house floor has none in, the 10 yr old part has 100mm. Both floors feel as cold as each other. It's easy to get absorbed in figures but having UFH makes sense to insulate better.

5 hours ago, crispy_wafer said:

Similar floor buildup as what I've got in progress.

 

Block and beam, 150mm of PIR, 60mm screed at the front door threshold - which is 15mm from memory.  I just went with what the door manufacturer recommended, in reality I should have waited and perhaps specified a slighty larger threshold.

 

When measured from the top of PIR to bottom of the door I have about 85mm so I've got a good 25mm for flooring depending on how flush I want the flooring to be.  I've settled on recessing a mat at the door opening, and glue down bamboo flooring @ 14/15mm so should work out ok.  Depending on thickness of mat I will grind out 5-10mm from the screed.

Was it the inside of the LL threshold that sits 15mm on top of the brickwork? This is what the aluminium ones seem to be on a search. It will be a UPVC door so not sure if it's the same? LABC site says maximum 15mm height difference or you require an internal ramp. I won't know if Im using tiles or karndean until built which will add or remove 15mm by which time it's too late. 

[ruggers]

@Temp@Canski 
Thanks for the diagram. With that diagram it's a slab floor so you can easily add more hardcore or concrete to get to your desired finish height.
Beam & block seems to work a brick course at a time so you either have to increase insulation or screed.

The screed is only supposed to be 50mm. I've allowed 60 in certain areas for any irregularities.

I can't lower outside FFL because theres limited fall for drainage so the house would have to go up but outside isn't really a concern. I was aiming for 150mm (2 bricks) step down from inside to outside on my other doors as it's nicer than 3 bricks & as per below sketch, bricks 3,4,5 line up with the 225 block sat on the beams. If I use 190mm insulation then add screed, this puts my inside FFL at well above the DPM door threshold that needs to be level. adding another brick would mean I need 300mm of make up from the beams unless I'm missing something?

 

[Canski]

I always determine the finished screed level then add the screed the insulation and the total B&B floor make up to determine the height of the bottom of the B&B. Sometimes this doesn't work courses but I make it work.

 

From your sketch I see that you have 200 / 210 mm above the top of your 150 b&B this would leave your DPM approx 15 - 25 mm above the top of your screed. The skirting would cover this. your insulation would extend to the outer skin of brickwork at door openings or use a design like Temps above. To facilitate this you need to start forming the openings at the top of your trench blocks on the inner skin only. This would enable the insulation and screed to run up to the brickwork or rather to the thermal break that you install on the inside of the brickwork where the opening is. or to the back of the door cill like Temps design above.

 

I hope this helps

[ETC]

Get your SE to design a reinforced slab. Gets rid of the sub-floor void and all ventilation terminals.

[ruggers]

1 hour ago, Canski said:

I always determine the finished screed level then add the screed the insulation and the total B&B floor make up to determine the height of the bottom of the B&B. Sometimes this doesn't work courses but I make it work.

 

From your sketch I see that you have 200 / 210 mm above the top of your 150 b&B this would leave your DPM approx 15 - 25 mm above the top of your screed. The skirting would cover this. your insulation would extend to the outer skin of brickwork at door openings or use a design like Temps above. To facilitate this you need to start forming the openings at the top of your trench blocks on the inner skin only. This would enable the insulation and screed to run up to the brickwork or rather to the thermal break that you install on the inside of the brickwork where the opening is. or to the back of the door cill like Temps design above.

 

I hope this helps

I think what your referring to where you open up the inner leaf lower down is to allow the slab to bridge the cavity to support the insulation and screed above and prevent cracking. If using B&B, this can be done by either cantilevering the beams out to the inside of the outer skin to support all above, or take a risk & only cantilever the insulation out to support the screed & hope it doesn't crack over time as per attached image taken from someone else's post on here. 

I really wouldn't care about the inside FFL being 20 or 50mm below the door threshold, all of my doors now have 50-70mm UPVC step overs, it's just because building controls involved with it being a new build. As per my sketch above, I could add 160mm insulation to bridge the gap a little, it's just what to do if i have to add 190mm insulation. I think i jus need to avoid this at all costs is the solution i'm coming to or be prepared to add 220mm of insulation if I want to keep the screed at 60mm. it's a numbers game.😒

26 minutes ago, ETC said:

Get your SE to design a reinforced slab. Gets rid of the sub-floor void and all ventilation terminals.

Ground clay heave issues so he wants suspended beams & deeper founds where trees were. Just paid extra for this after person who done the plans said heave wouldn't be an issue while not knowing the ground. Don't ask.

[Andehh]

160mm recticel achieves 0.11...might be a fair compromise? It's 10% higher performing then Kingspan equivalent. 

[Canski]

Or fill cavity below the void up to the underside of b&b. And then fill with PIR up to your floor insulation. 

[Dave Jones]

you want 150mm insulation 75mm screed to make 225 to match external brickwork.

 

EPS insulation is cheaper by far.

[ruggers]

13 hours ago, Andehh said:

160mm recticel achieves 0.11...might be a fair compromise? It's 10% higher performing then Kingspan equivalent. 

I'll look into that, 0.11 is fine, no ones policing it. Its actually cheaper to buy 100mm and a 50/60mm than it is to buy a 150mm. Strange.

11 hours ago, Canski said:

Or fill cavity below the void up to the underside of b&b. And then fill with PIR up to your floor insulation. 

Has to be minimum 150mm air gap below the beams

3 hours ago, Dave Jones said:

you want 150mm insulation 75mm screed to make 225 to match external brickwork.

 

EPS insulation is cheaper by far.

Liquid screed is best reaction times at 50mm, EPS requires 30% more to achieve same U-value as PIR but good shout to make up the height difference if I add another brick making it 300mm.

 

 

[ruggers]

I think I have a good few options now to work to, just interested to know, if i use B&B for the garage floor which will sit 150mm lower than the attached house. What finish do you normally add to the beams and what thickness to avoid cracking as no insulation is required in there.

[Canski]

2 hours ago, ruggers said:

 

Has to be minimum 150mm air gap below the beams

Liquid screed is best reaction times at 50mm, EPS requires 30% more to achieve same U-value as PIR but good shout to make up the height difference if I add another brick making it 300mm.

 

 

That’s true but under the whole floor not just the doorways. I really can’t see the problem here. Everyone has openings in beam and block floors. They are all dealt with in the same way or not ? Preserve your build envelope by installing continuous insulation. There will always be a cold(er) spot at thresholds in one way or other. It’s about how you deal with the other 99% 

[Dave Jones]

8 hours ago, Canski said:

That’s true but under the whole floor not just the doorways. I really can’t see the problem here. Everyone has openings in beam and block floors. They are all dealt with in the same way or not ? Preserve your build envelope by installing continuous insulation. There will always be a cold(er) spot at thresholds in one way or other. It’s about how you deal with the other 99% 

 

you could allways use marmox blocks at thresholds to mitigate cold bridging.

 

Personally prefer 75mm min of sand/cement/fibre screed over flowscreed anyday. more thermal mass, more accurate.

[ruggers]

@Canski I was referring to the whole ground floor not just the door thresholds if thats the way it sounded. I was just focussing on heights around LL door openings as thats where the FFL needs to align with.

I've just had a look on one site at EPS jablite and it's double the price of PIR while the PIR is competitively priced.

[jon-lee]

On 25/10/2022 at 12:48, ruggers said:

I have some house plans approved for a masonry build which now need to switch from slab floor construction to beam and block which I've never used before.

 

I'm having trouble understanding how you align the inner and outer leaf brick courses so that the inside finished floor height is level with the cavity wall DPC that the external doors will sit on. If I add a 225mm inner leaf block on top of the beams & then use 150mm floor insulation on top of the beams + 50/60mm screed, it works out well at 210mm, which is under the 225mm block DPC level and leaves some room for tiled floor surface before the low door threshold. This makeup = 0.12W/m2k
 

My SAP has specified 0.10W/m2k using 150mm PIR which you can't achieve, it would require 190mm insulation which throws the heights out a lot.

190mm insulation + 50/60mm of liquid screed = 250mm or 270mm with a tile. This sits higher than a block but 30-50mm too low for a block and a brick to match DPC.

 

How do you make up the floor levels to match low level door threshold/DPC, is it a case of you have to add more insulation and more screed to get to 300mm DPC? With a slab floor you can offset the height of the slab to suit so I could have any thickness of insulation.

 

Is 0.10 vs 0.12 W/m2K a massive difference in a heat loss calculation or noticeable in the real world?

 

I planned on having 150mm two brick courses step down to my outside finished floor level with the exception of the front door which is a ramped access low threshold to comply with regs.

 

From the top down, my floor make up is,

Minimum 50mm liquid screed containing wet underfloor heating (May need to be 60mm in some places to account for 10mm curve on beams)

150 or 190mm PIR insulation. 

150mm concrete T beams with 100mm block infill and 50mm slip bricks.
 

If you're using a beam and block floor I'd increase the screed to 75m as the beams are prestressed creating a camber as much as 25mm at midspan, this will vary depending what infill blocks are used and finishes. My opinion not advice 

[ruggers]

@jon-lee Once i get them in I'll set the leser up and have a check across the rooms. Spans vary from 3.8, 4.25, 4.9, 2.5m. Thats including the 100mm end bearing. I'll be using dense solid blocks as the lighter more insulating ones don't offer any more to the U-Value. 

 

the reason I was going with 50mm liquid screed was initially because of the faster reaction times but thisn't so much of an issue with weather compensation. It's just the extra 25mm of cem floor adds quite a lot onto the price for every 5mm thicker but I do see what you mean if theres a lot of bow in them.

[Dave Jones]

go for 300mm EPS. cheap and good bang for the buck. You have the room already. 

 

simplify your buildup. trench block + concrete common then beam on top.