Insulated threshold detail for insulated rafts

[WannabeBob]

Hi hive mind, we are just about to start our ground works next week, so cue me trying to schedule delivery for all the foundation parts when whoops I’ve just found a small detail that’s fallen through the cracks somewhat.

 

Our door threshold details have been specified in conjunction with Internorm who are our window supplier. This is the detail we have from our architect:

 

which is based on Internorm’s standard detail.

 

All well and good except Internorm wants the threshold to be fixed into the structure to prevent it from moving. Their standard detail won’t work with our setup as the bracket is meant to anchor it into the base, which is EPS for us and wouldn’t really hold a bolt…

 

So we’ve now had the buck handed between Internorm, the window installers, architect, and now structural engineer, with each of them saying it’s someone else’s responsibility to figure out what to do in our case.

 

Internorm have confirmed that the anchors don’t hold the weight of our doors, as that load gets transferred downwards. It’s only there to prevent it from moving. 

 

I suspect something like a J anchor fixed to the inside face and cast in place with the concrete should do, and we’re trying to confirm that’s fine with all parties involved, but I was wondering what have others done in a similar situation?

Edited March 31 by WannabeBob

[Nick Laslett]

@WannabeBob, great post. I hope you get some good replies. 
 

There are so many instances like this, where no matter how much you prep, in the real world there needs to be some workaround compromise. I don’t know if CT1/OB1 would be strong enough to hold the door? My go to solution for many parts of my build. 
 

My passive foundation upstand is only 90mm thick, so the door could still be fixed to the concrete, but they had to compromise with how the Sill would be fitted, because the door was set back. 
 

The only issue, is if the warranty or workmanship isn’t being owned by someone. 

[WannabeBob]

Thanks Nick. To be honest, I hadn’t considered adhesives. It will mean we can leave it till after the concrete pour for the window installers to fix the threshold, which would simplify the warranty / workmanship aspect. Using cast in place, we’d need to get our groundworkers to do this which might open ourselves up to a bit of finger pointing if something does go wrong. 

 

Something to check with them!

[Nickfromwales]

Speak to Sika and see if any of their family of Sikaflex mastics would be better here. 
 

Rainwater management will be the constraint here, but possibly won over if you use (prob defo need to) a continuous bead on the inside, and then a stop start bead on the outside to allow drainage. 
 

There’s a lot going on in that pic, if you look closely.

[WannabeBob]

47 minutes ago, Nickfromwales said:

Speak to Sika and see if any of their family of Sikaflex mastics would be better here. 
 

Thanks! I’ll check with them. 

 

47 minutes ago, Nickfromwales said:

 

Rainwater management will be the constraint here, but possibly won over if you use (prob defo need to) a continuous bead on the inside, and then a stop start bead on the outside to allow drainage. 

I’m sure I’m flaunting my ignorance here, but shouldn’t the DPC that we’re overlapping on the upstand prevent water ingress behind the upstand? Or is this a belt and braces thing, though I’d have thought if water did get behind it would be pooling behind the DPC and we’re kind of **** anyway?

[Nickfromwales]

11 minutes ago, WannabeBob said:

Thanks! I’ll check with them. 

 

I’m sure I’m flaunting my ignorance here, but shouldn’t the DPC that we’re overlapping on the upstand prevent water ingress behind the upstand? Or is this a belt and braces thing, though I’d have thought if water did get behind it would be pooling behind the DPC and we’re kind of **** anyway?

I was referring to the drip in the threshold detail of the window / slider itself.  Check with the manufacturer to see if what I show is the drainage pathway, if so, all good and the threshold can be fully bonded down.

 

[Nick Laslett]

@WannabeBob, I use these insulation fixing from Fischer on my build a lot, because I have ICF walls. 
 

https://www.fischer.co.uk/en-gb/products/fixation-on-etics-insulation/fixing-in-insulation-material

Rawlplug also have a version. They screw into the EPS/XPS the FID II plus 80 can take 0.20kN of force, which equals 20kg weight. 

https://rawlplug.co.uk/product/r-iso-plug-insulation-fixings/

 

I prefer the shorter fixing from Fischer and the long one from Rawl. 
 

 

I was skeptical about how secure they were, but did a test with the 80mm fixing in the EPS300 and was surprised with how much force they could take. This was just the fixing, no adhesive.
 

When I finish my build, I plan to make a few YouTube videos testing some of the EPS ICF fixing solutions I tried. 

 

Edited March 31 by Nick Laslett

[WannabeBob]

27 minutes ago, Nickfromwales said:

I was referring to the drip in the threshold detail of the window / slider itself.  Check with the manufacturer to see if what I show is the drainage pathway, if so, all good and the threshold can be fully bonded down.

 

 

Got it now, thanks!

 

20 minutes ago, Nick Laslett said:

<snip>

 

Thanks! Not sure if I’ll use those for the threshold, but useful info nonetheless, as we’ll be having ICF walls too. 

[Alan Ambrose]

Very topical, I’ll be wrestling this detail in about 5 minutes…

 

Resin anchor into side of slab? Also, it’s struck me that the fixing strips around the top and sides of the door could take some shear load - I think generally they just hold the door in place against wind loads etc.

[IanR]

13 hours ago, WannabeBob said:

 

which is based on Internorm’s standard detail.

 

All well and good except Internorm wants the threshold to be fixed into the structure to prevent it from moving.

 

 

I don't know of the Internorm "thermoplastic insulated threshold", but the image above shows it taking bolted/screwed fixing so I'd put the brackets on to the threshold and suspend the lower portion in air, where you are going to cast the raft. Put some threded bar through the holes in the (initially) unattached end, using a nut either side to hold the threaded bar in position, then cast the bracket into the raft.

 

 

You'll have to temporarily, externally, back up the threshold so that it doesn't move during the pour.

Edited Tuesday at 06:42 by IanR

[Nickfromwales]

If you have a local metal fabricator then you could take the brackets to them and ask them to attach (stud-weld) some 6 or 8mm studs to them, one 40mm down from the top, and one 30mm up from the bottom. 
 

Then use barrel nuts to screw onto the studs, then threaded bar (300mm long?) into those barrels to give you some length for purchase in the concrete.

 

A good deal of type 1 or other haunching  outside will hold everything in place curbing the pour, but that will require a lot of thought and preparation for prevention of any movement, and baby sitting to prevent the “oh, it’ll be fine” attitude of others who won’t realise that a few mm out is disastrous. 

[saveasteading]

I wouldn't want the door in place before the concrete pour. It will likely be damaged.

 

So I think I favour keeping the slab low at that point. Same height as the block, or a little lower, perhaps 100 or so wide?

You could chance remembering to keep it low by hand finishing,  or put a shutter there, my recommendation.

Then the bracket bolts down to really solid concrete.

[WannabeBob]

10 hours ago, Alan Ambrose said:

Very topical, I’ll be wrestling this detail in about 5 minutes…

 

Resin anchor into side of slab? Also, it’s struck me that the fixing strips around the top and sides of the door could take some shear load - I think generally they just hold the door in place against wind loads etc.

 

Passivhaus consultant is keen to avoid a bolt through the upstand to avoid point thermal bridges. There 25 of those over all the doors so not quite insignificant? Otherwise resin anchors would be appealing. 

 

53 minutes ago, IanR said:

 

 

I don't know of the Internorm "thermoplastic insulated threshold", but the image above shows it taking bolted/screwed fixing so I'd put the brackets on to the threshold and suspend the lower portion in air, where you are going to cast the raft. Put some threded bar through the holes in the (initially) unattached end, using a nut either side to hold the threaded bar in position, then cast the bracket into the raft.

 

 

You'll have to temporarily, externally, back up the threshold so that it doesn't move during the pour.

 

The “thermoplastic” I think of essentially purenit on the faces bonded to some kind of insulation in the middle. not quite sure what that insulation is made of. 

 

I think your idea sounds similar to a J bolt? But it’s made me think if we could do the slab pour in 2 lifts? First lift then anchor down the brackets into it, then the full lift. Don’t know if that causes issues with the slab?

 

32 minutes ago, Nickfromwales said:

If you have a local metal fabricator then you could take the brackets to them and ask them to attach (stud-weld) some 6 or 8mm studs to them, one 40mm down from the top, and one 30mm up from the bottom. 
 

Then use barrel nuts to screw onto the studs, then threaded bar (300mm long?) into those barrels to give you some length for purchase in the concrete.

 

A good deal of type 1 or other haunching  outside will hold everything in place curbing the pour, but that will require a lot of thought and preparation for prevention of any movement, and baby sitting to prevent the “oh, it’ll be fine” attitude of others who won’t realise that a few mm out is disastrous. 

 

17 minutes ago, saveasteading said:

I wouldn't want the door in place before the concrete pour. It will likely be damaged.

 

So I think I favour keeping the slab low at that point. Same height as the block, or a little lower, perhaps 100 or so wide?

You could chance remembering to keep it low by hand finishing,  or put a shutter there, my recommendation.

Then the bracket bolts down to really solid concrete.

That bit about keeping the threshold in place during the pour is one of my big concerns too. Would there be any issues with pouring the slab in phases?

[saveasteading]

34 minutes ago, WannabeBob said:

Passivhaus consultant is keen to avoid a bolt through the upstand to

Really? Ask for a thermal loss calculation or estimate. Instinct tells me this is de minimus.

 

I would rather lose 10p worth of heat there per annum than have a loose door.

 

If playing that game, use skinny fixings into plastic plugs.

 

37 minutes ago, WannabeBob said:

pouring the slab in phases

 

Easy. You can build a timber shutter there from stud and plywood. Then remove it and put in local concrete to whatever level you choose. It's about 3 shovels worth, hand mixed.

You have total control of fixing the bracket, and precision.  

An old fashioned way is a lump of eps. Then you rake it out or, naughtilly, use petrol. 

 

43 minutes ago, WannabeBob said:

keeping the threshold in place

I'm more worried about groundworkers next to a nice door. Bumping , splashing.  They might even barrow or pump through the open door.

Take the risk out of it. Door later.

[WannabeBob]

3 hours ago, saveasteading said:

Really? Ask for a thermal loss calculation or estimate. 

I suspect if push came to shove we’d be able to do that, but just exploring options at this point

 

3 hours ago, saveasteading said:

 

I'm more worried about groundworkers next to a nice door. Bumping , splashing.  They might even barrow or pump through the open door.

Take the risk out of it. Door later.

Right, the doors themselves are only going to be installed much later when the walls and roof is up. It’s only the threshold/upstand that might get installed during the concrete pour. The doors then sit on those upstands. 

 

I get the mechanics of shuttering then filling in the void, but won’t this create a section that isn’t bonded together as well as a continuous pour? Or does it not matter really?

[saveasteading]

1 hour ago, WannabeBob said:

does it not matter really?

Not really. 

Especially if it is partial depth.

 

What I'd do is a lump of eps, about 100 x 100. Fix it to the threshold wall at floor level. Your concrete pour will fill under it, giving you continuity. You will have a 100mm void for your brackets.

 

Draw this to scale  and check you can get the fixings in.

[Nick Laslett]

4 minutes ago, saveasteading said:

Not really. 

Especially if it is partial depth.

 

What I'd do is a lump of eps, about 100 x 100. Fix it to the threshold wall at floor level. Your concrete pour will fill under it, giving you continuity. You will have a 100mm void for your brackets.

 

Draw this to scale  and check you can get the fixings in.

Great suggestion. I did a few areas of my slab where we had EPS in place to be removed later. We used this approach to drop the threshold level for the patio doors. 
 

@WannabeBob, you should try to avoid having any finished parts of the house in place until as late as possible. 

[WannabeBob]

23 minutes ago, saveasteading said:

Not really. 

Especially if it is partial depth.

 

What I'd do is a lump of eps, about 100 x 100. Fix it to the threshold wall at floor level. Your concrete pour will fill under it, giving you continuity. You will have a 100mm void for your brackets.

 

Draw this to scale  and check you can get the fixings in.

Thanks, that sounds like it might be the way to go about it then. 

 

16 minutes ago, Nick Laslett said:

Great suggestion. I did a few areas of my slab where we had EPS in place to be removed later. We used this approach to drop the threshold level for the patio doors. 
 

@WannabeBob, you should try to avoid having any finished parts of the house in place until as late as possible. 

Yeah we are doing that for the ground floor wetroom too, but wasn’t too sure if this being at the edge would cause issues. It sounds like i’m worrying too much about that though.