General: Door threshold detailing

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- CommentAuthorSimonD
- CommentTimeJan 9th 2021 edited
I'm currently installing my new windows and doors. Perplexingly I have detailing for weather and air thightness for pretty much everything in my build apart from these thresholds.

Any suggestions on how best to detail these? (image attached)

The plan is to mount onto continuous marine ply spacers to bring the threshold just above finished floor level. For all the windows I'm using Soudal SWS with exterior seleant, expanding foam and interior airtightness sealant.
- CommentAuthorSimonD
- CommentTimeJan 9th 2021 edited
Photo
- CommentAuthortony
- CommentTimeJan 9th 2021
I donâ€™t like the idea of wood under thresholds.
- CommentAuthordjh
- CommentTimeJan 9th 2021
I don't understand what I'm looking at in the photos? Why does whatever it is have smears of what looks like glue on it?

Our doorsets came with built-in wooden thresholds. We've put oak extenders in front in the odd case where we needed something. The doorsets are secured by screws through the sides, and the threshold just floats. I packed some ordinary EPS pieces underneath to give them a bit of support and we haven't noticed any flexing or other problems.

Windows were screwed into OSB 4-sided 'boxes' and the boxes secured to uprights in the walls. The bottom side of the box just sits on the straw bale underneath in our case. There is tape (Pro Clima Tescon Profil) connecting the window to Contega PV that is plastered in around the top and sides. The bottom has a piece of DA membrane under the window board again with Contega PV around the edges.

Details will of course vary depending on what the structure around them looks like. Did an architect or designer prepare the drawings? If so, go back and ask for the missing ones PDQ!
- CommentAuthorSimonD
- CommentTimeJan 9th 2021
The photos were to show the profile of the aluminium thresholds of the two types of doorsets. The remnants of glue are just from manufacturing, made worse from some site dirt and rain while I've been braking up the crates. The doors are currently sat on the pallets.

I'm good with all the detailing with the various rough openings, some of which are timber frame, some are extended out from existing masonry for retrofit ewi so I used a similar approach to your osb - although im my case I've used fixing straps back to the masonry and have a plywood box about the window frame which sits outside the existing walls.

In terms of detailing, I've done it all myself for this house. In my view, my architect was so wholly inept at producing anything anywhere close to acceptable in terms of detail/construction drawings it was an embarassment to the profession. I think one of our last conversations went along the lines that there is no point producing detailed drawings because the builders will decide how to do it so it's better just to leave them to it. I always wondered how one specifies a contract that way but he remained silent on that one. Mind you, he was good at the design where he had good insight and he was very good with the planners, so some blessings there.

The only bit of the detailing that I'm curious about hence my question is the thresholds specifically and whether I need to seal up the exterior and interior sides of the threshold for weather ingress or airtightness respectively. My concern is that if I merely let the thresholds rest as they are, I'm potentially leaving a weak point for air leakage, for example. Each of the thresholds do have a drip edge which sits outside the frame, it's just this final little detailing playing on my mind.

Hope that makes sense.
- CommentAuthordjh
- CommentTimeJan 10th 2021
Posted By: SimonDThe only bit of the detailing that I'm curious about hence my question is the thresholds specifically and whether I need to seal up the exterior and interior sides of the threshold for weather ingress or airtightness respectively. My concern is that if I merely let the thresholds rest as they are, I'm potentially leaving a weak point for air leakage, for example. Each of the thresholds do have a drip edge which sits outside the frame, it's just this final little detailing playing on my mind.

Yes, you need to seal up the outside to be weathertight (at some point, it is possible that the outer part of the threshold is designed to get wet and drain to the outside as often as it likes). And wherever your airtightness layer is, yes you need to seal the threshold to the surrounding airtightness layer, just like the rest of the frame. But that sounds so obvious I can't believe that's what you're asking - I must have misunderstood.
- CommentAuthorrevor
- CommentTimeJan 10th 2021
I append sketch of what I would do and have done. Support on timber bearers sandwiching insulation to make a thermal break. If not happy with timber use recycled plastic timber. Timber is easier to dimension though. You can also seal the joint under the threshold front with EPDM bonded with sealant recommended if you are in an exposed area makes it rain and windproof. (See ARBO website for products) On my house I finished off with a slate cill. All my doors and windows are set back from the front of the house sitting at the cavity. Frame sides / top fill with expanding foam, acrylic sealant and then tape sides to inner wall to go behind plaster board. I used Tyvek acrylic tape but others available
- Frame sealing detail.pdf
- CommentAuthorSimonD
- CommentTimeJan 10th 2021 edited
Posted By: djhBut that sounds so obvious I can't believe that's what you're asking - I must have misunderstood.

Yes, I know it's so obvious it's unbelievable. I feel exactly the same, and know I'm asking a stupid question, yet out of all the detailing I have; copious information from insulation suppliers, window supplier etc. there's not a jot about proper detailing of the actual door threshold for weather and air tightness. Even my construction books leave this out. The only one that does cover a threshold is a firstand secondfix carpentry manual but that's just a typical bog standard hardwood threshold on masonry. Oh, and I've spent plenty of time on Google one result of which from greenbuildingadvisor.com says along similar lines:

"Itâ€™s easy to find advice on flashing windows. But what about exterior doors? For some reason, most construction experts havenâ€™t provided builders with much advice about flashing doors."

So that's my initial question and bemusement sorted out then! I haven't totally lost the plot.

I've got a slightly different situation in that my house is an upside down house, thus, for example, my french doors are to be installed on a first floor glulam ring beam where they open out onto a bridge. Additionally, due to ewi neither of the other doors sit in masonry walls as they're extended out from the walls and sitting on timber.

Okay, so with that thinking aloud, I've now expanded the question from 'it's needed?' to how I'm I going to solve this particular problem

I need some kind of weather-check to the inside of the threshold and some flashing so that any water ingress can drain to outside. So in answer to my own question then, I think it makes most sense to first fashion up some flashing. My woodfibre ewi manufacturer suggests aluminium tape flashing below window sills but I'd be concerned about longevity of this under a door threshold. I think I will fashion up a metal flashing from some sheet aluminium. Then I can simply install breather membrane on the timber, flashing, then door set and seal for weather and airtightness to the back of the pan where it would fold up behind the door threshold. I then have air tighness and water drain to the outside.

Any thoughts?

Thanks!
- CommentAuthorrevor
- CommentTimeJan 10th 2021
There are no stupid questions, well there is one, and that is the one you did not ask.
- CommentAuthordjh
- CommentTimeJan 10th 2021
Posted By: SimonDYes, I know it's so obvious it's unbelievable. I feel exactly the same, and know I'm asking a stupid question, yet out of all the detailing I have; copious information from insulation suppliers, window supplier etc. there's not a jot about proper detailing of the actual door threshold for weather and air tightness. Even my construction books leave this out. The only one that does cover a threshold is a firstand secondfix carpentry manual but that's just a typical bog standard hardwood threshold on masonry.

Ah, when you wrote 'details' I took that to mean the detail drawings for your particular house, rather than general details. Apologies! Yes, I had to make up the arrangement I described when I realized that there weren't any existing. With our doors the critical realization was that the threshold doesn't support any static load at all, just the dynamic load of people and things walking or rolling over it. Except for the lift-and-slide patio door, which requires a completely flat and solid support underneath to make it work (otherwise it jumps off its track - don't ask me how I know ) Fortunately we had a handy thermally insulated concrete slab in the right place.

I need some kind of weather-check to the inside of the threshold and some flashing so that any water ingress can drain to outside. So in answer to my own question then, I think it makes most sense to first fashion up some flashing. My woodfibre ewi manufacturer suggests aluminium tape flashing below window sills but I'd be concerned about longevity of this under a door threshold. I think I will fashion up a metal flashing from some sheet aluminium. Then I can simply install breather membrane on the timber, flashing, then door set and seal for weather and airtightness to the back of the pan where it would fold up behind the door threshold. I then have air tighness and water drain to the outside.

Sorry, I'm still having trouble visualising it all. FWIW, my airtightness layer is basically the interior plaster on the outside walls and the concrete floor slab. So the threshold has Tescon Profil stuck to its inside edge and taken down to the slab by more strips of tape where yet more tape is stuck to the slab with Pro Clima primer. I can't actually remember what we put at the outside edge, maybe some more tape of the weatherproof variety? But the outside edges are protected from the worst of the weather by external materials with a narrow drain slot between. The patio, the front steps, an oak sill extender, etc.
- CommentAuthorSimonD
- CommentTimeJan 10th 2021
Posted By: revorI append sketch of what I would do and have done. Support on timber bearers sandwiching insulation to make a thermal break. If not happy with timber use recycled plastic timber. Timber is easier to dimension though. You can also seal the joint under the threshold front with EPDM bonded with sealant recommended if you are in an exposed area makes it rain and windproof. (See ARBO website for products) On my house I finished off with a slate cill. All my doors and windows are set back from the front of the house sitting at the cavity. Frame sides / top fill with expanding foam, acrylic sealant and then tape sides to inner wall to go behind plaster board. I used Tyvek acrylic tape but others available
- http://www.greenbuildingforum.co.uk/newforum/?PostBackAction=Download&AttachmentID=7752" >Frame sealing detail.pdf
Thanks for that, that's helpful. I must have missed this earlier while I was drafting myother note and having some lunch!
- CommentAuthorSimonD
- CommentTimeJan 10th 2021
Posted By: djh
Sorry, I'm still having trouble visualising it all. FWIW, my airtightness layer is basically the interior plaster on the outside walls and the concrete floor slab. So the threshold has Tescon Profil stuck to its inside edge and taken down to the slab by more strips of tape where yet more tape is stuck to the slab with Pro Clima primer. I can't actually remember what we put at the outside edge, maybe some more tape of the weatherproof variety? But the outside edges are protected from the worst of the weather by external materials with a narrow drain slot between. The patio, the front steps, an oak sill extender, etc.

That is helpful to think about various ways to achieve it. I've attached a pdf of hastily modified drawing of some of my insulation details. I'm proposing to put some airtightnes tape to the inside of the plywood spacer threshold/threshold flashing.

BTW, not visible is that this whole area is well protected from weathering by a 500mm roof overhang.

Hope that helps to illustrate a bit better.
- door threshold detail.pdf
- CommentAuthorlineweight
- CommentTime5 days ago
More information is needed to help you properly here. Do you have no construction drawings for the project at all?

Questions I'd have:

- What type of door is it - can we see a cross section of the door sill? Things like where water drains from, where any thermal breaks are, and so on are important.

- Why EWI on a cavity wall? Is it a pre-existing cavity wall that's been retrofitted with EWI? Is there insulation in the cavity?

- Are the floor joists existing ones? In a cavity wall buildup I'd normally expect to see the floor structure bearing onto the inner leaf of the cavity... why is the 'ring beam' on the outer leaf and what does it do?

- What do you step out onto - you say some kind of bridge - is it supported off this wall or independently?

- In a way, because this is not at ground floor level, you are probably looking for something that's more like a windowsill detail than a threshold detail, because threshold details are usually dealing with a situation at ground level where you are thinking about the floor structure, and how the insulation envelope goes from wall to floor.

- Can you post an example of the detail you are using for the windows? I would use that as a starting point.

- Does this need to be a level threshold, for building regs? In other words do you need inside and out to be near enough the same level, and does it need to satisfy the regs for an accessible threshold?

- I assume you've asked the door/window supplier for advice, as a starting point? Some have pretty good libraries of standard details for a rang of different wall buildups, and some have virtually nothing. Maybe yours is in the latter category.

As a general comment - yes you are quite right that there can be a bit of a lack of standard solutions or advice when it comes to door thresholds. Or, at least, you'll find a lot of standard details that are simply out of date because they don't match (a) modern expectations for insulation and thermal bridging (b) more modern methods of construction such as EWI (c) those accessibility requirements for level thresholds and (d) modern doors and windows which often have things like drainage within the frames. In the olden days it was pretty much just plonk your frame on something solid and make sure water drains away... it is no longer so straightforward.

I'm interested that you have been looking at a kind of "tray" solution. It seems to me that it ought to be more of a "standard" thing you can get, but it isn't really. You might be interested in this thread:

http://www.greenbuildingforum.co.uk/newforum/comments.php?DiscussionID=15199&page=1#Item_15

I'm sorry your architect failed you on producing construction drawings. There's an element of truth in what he suggests, that for certain types of projects where everything is pretty much standard and the budget is low, then the builders are going to fairly much do what they want or what they are used to, and will barely look at construction details if they can get away with it and it's a bit of a lottery, whether they are going to have given any proper thought to stuff like thermal detailing.

But for any project that is not bog standard, and where you've got an ambition to get insulation right, absolutely you need some proper construction details. Making things up as you go along is not going to end well.
- CommentAuthorSimonD
- CommentTime5 days ago
Posted By: lineweightMore information is needed to help you properly here. Do you have no construction drawings for the project at all?

The closest thing I had to construction drawings were the drawings supplied by our structural engineers. Everything else I've drawn up myself.

Questions I'd have:

- What type of door is it - can we see a cross section of the door sill? Things like where water drains from, where any thermal breaks are, and so on are important.

The doors are 1) insulated timber door with timber frame with low level 25mm threshold, 2) triple glazed timber framed outward opening french doors with low level aluminium treshold, 3) inward opening triple glazed timber framed door with 25mm low level threshold.

- Why EWI on a cavity wall? Is it a pre-existing cavity wall that's been retrofitted with EWI? Is there insulation in the cavity?

Because the pre-existing cavity wall didn't have sufficient or clean enough cavity to retrofit cavity wall insulation and wouldn't provide sufficient insulation anyway - been there done that on an old property and won't do it again.

- Are the floor joists existing ones? In a cavity wall buildup I'd normally expect to see the floor structure bearing onto the inner leaf of the cavity... why is the 'ring beam' on the outer leaf and what does it do?

None of the existing joists exist any more. First floor joists are completely new and hang off the glulam ring beam, ground floor joists are now fixed to bearers bolted to the inner leaf. The ring beam is on the outer leaf in order to bring the first floor timber frame into better alignment with the ground floor wall with ewi. The ring beam is part of the structural scheme to support the newly built timber frame first floor.

- What do you step out onto - you say some kind of bridge - is it supported off this wall or independently?

Yes, it's supported off the outer leaf of the wall - two substantial universal columns with timber decking.

- In a way, because this is not at ground floor level, you are probably looking for something that's more like a windowsill detail than a threshold detail, because threshold details are usually dealing with a situation at ground level where you are thinking about the floor structure, and how the insulation envelope goes from wall to floor.

- Can you post an example of the detail you are using for the windows? I would use that as a starting point.

I think I'm slightly beyond that one already simply due to the interface between the first floor and the ground floor ewi. Interestingly I may have found a similar solution within the detailing manual provided by the ewi manufacturer where there's a french door opening onto decking and has an extend aluminium flashing.

I don't have the detailing for the windows electronically. I'm primarily using the details provided by the window company with the delivery for insertion into a timber frame and those provided by the ewi manufacturer for install into the ewi.

- Does this need to be a level threshold, for building regs? In other words do you need inside and out to be near enough the same level, and does it need to satisfy the regs for an accessible threshold?

No need to satisfy regs for accessibility but we have chosen low level thresholds.

- I assume you've asked the door/window supplier for advice, as a starting point? Some have pretty good libraries of standard details for a rang of different wall buildups, and some have virtually nothing. Maybe yours is in the latter category.

Yes, good window stuff but not enough for doors. They have provided the reference for additional technical door detailing but I will have to buy it from the Norwegian building research institute.

... it is no longer so straightforward.

No, certainly isn't.

I'm interested that you have been looking at a kind of "tray" solution. It seems to me that it ought to be more of a "standard" thing you can get, but it isn't really. You might be interested in this thread:

http://www.greenbuildingforum.co.uk/newforum/comments.php?DiscussionID=15199&page=1#Item_15

Yes, I experimented with it this week when installing the front doorset. Basic build up was to space door height relative to finished floor level with marine plywood, flashed this with alumimium flashing tape on top of which I installed an aluminium tray that I fabricated from some thin sheet aluminium and then sealed up.

I'm sorry your architect failed you on producing construction drawings. There's an element of truth in what he suggests, that for certain types of projects where everything is pretty much standard and the budget is low, then the builders are going to fairly much do what they want or what they are used to, and will barely look at construction details if they can get away with it and it's a bit of a lottery, whether they are going to have given any proper thought to stuff like thermal detailing.

But for any project that is not bog standard, and where you've got an ambition to get insulation right, absolutely you need some proper construction details. Making things up as you go along is not going to end well.

One of the last conversations I had with my structural engineer was when I asked him if we could change a detail. His reply was that it was fine if not quite a standard approach "but then nothing with your build is standard." When I realised my architect wasn't up to the job I started doing all the research I needed to complete the technical detailing myself so I definitely haven't had to make things up as I go along. But as with all these things and because I'm also building it all myself there are always some things that crop up where you've overlooked a detail.

Thanks for your input.
- CommentAuthorlineweight
- CommentTime4 days ago
It's a bit difficult to offer much in the way of ideas, without seeing the exact profiles for the door sills/thresholds. They sometimes are designed with a kind of notch that you can turn a flashing up into, meaning that you can be confident of a good seal from outside, without doing the "tray" type thing where the flashing runs underneath the whole thing and then turns up behind.

One of your issues I guess is how to get across the EWI layer, because the standard type of flashing there - that you might find at a window sill - will not be designed to be stepped upon.

Therefore my strategy might be to move that flashing downwards sufficiently that the edge of your decking cantilevers a little, over the EWI layer, so you are stepping directly from solid internal floor to decking outside, with just the door threshold itself inbetween. This also means that whatever flashing that tucks under your doorframe threshold can turn immediately downwards, removing worries about water sitting on a flat-ish area just outside the sill.

The obvious problem this then presents is how to ensure continuity of the insulation layer, between the top of the EWI and the doorframe. If you were building immediately off blockwork I might suggest a layer of compacfoam or other similar materials that have been discussed in other threads here. But it seems that in this case it's predetermined that you will be sitting on the glulam beam. Is there scope for some insulation inside of it?

Of course... what happens further along the wall, where you are transitioning from EWI to timber frame will be relevant. Again from a general detailing strategy point of view... I would be looking to make that top flashing over the EWI a uniform line horizontally - so it is essentially the same whether its running under the door area or not - and then what is happening immediately above it changes according to location. In other words, try and de-couple that detail from what needs to happen at the threshold. Does that make any sense?

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