Front door level threshold detail

[Dave Anderson]

Hi all,

Our new build bungalow is underway - walls are up to DPC and beam & block is in.  I have been puzzling for ages over the front door threshold.  I have read a lot of posts here and elsewhere, and nothing ever quite fits my scenario.  I have tried to understand the principles and have come up with my own detail which is shown below.  I would appreciate any comments, criticisms or advice anyone can offer.  Balancing insulation requirements, airtightness, watertightness, structural needs and aesthetics in a level threshold design seems to be a black art.  We have no architect on board - we have preferred to carry out all design work ourselves (for better or worse). 

 

We have a masonry cavity wall with 150 cavity (50 air gap and 100 PIR).  The outer skin is natural stone, with cut stone window surrounds and jambs to the front door.  I do not like extended aluminium thresholds so am proposing a cut stone cill as shown.  Endurance have shown me a number of their threshold options, the neatest of which in my opinion is a Macclex section which has a minimal aluminium projection externally which should throw water down onto the stone cill.

 

The thing I am struggling the most with is providing adequate structural support to the threshold.  I want to position the frame 50mm into the cavity, so it will not really be supported by the stone cill.  I don't want to widen the stone cill to support the threshold, as it would be a cold bridge.  Compacfoam or similar seems to be the way to go.  But what supports the Compacfoam?  This is solved in my design by filling the cavity with concrete to beam and block level and sitting the Compacfoam on that.  

 

Many thanks for reading this.  I'd be very grateful for any comments or pointers.

 

[Russell griffiths]

Yep that works. 

[Dave Anderson]

Thanks Russell. I've been a little concerned about the stability of the stone cill - if someone put all their weight on the leading edge it will tend to rock.  I suppose the stone jambs at each end of the cill should hold it down ok, but I might pull the drainage channel forward and make sure it is offering some additional support.

[Russell griffiths]

Didn’t look at the cill. 
 

do you need a drainage channel, is there not a porch roof or something above the door, I would only have the channel if you think you will be getting a fair amount of water there. 

[Dave Anderson]

Umm, fair point. There will be an oak porch, but with open sides, so some rain will blow in. The roof of the porch is 2.6m wide, so about 0.9m past each edge of the door. So probably unnecessary then. Thanks for flagging that up.

 

[bassanclan]

In a similar situation to you I used this:

https://www.marchesironmongery.co.uk/exitex-mwk-r-2-20-weatherbar-mill-various-lengths.html

 

(Got it a bit cheaper from  website called Hebden & Holding)

I set the stone cill 10-15mm higher, removed the front sloped section from the floorbar and the piece that you fix to the face of the door. You can just see a narrow black rubber strip along the bottom now, so minimal aluminium on show

[Dave Anderson]

Thanks bassanclan, I'm sure that would look better. Only concern might be if any water does get into the threshold strip, where can it drain to?

[bassanclan]

3 hours ago, Dave Anderson said:

Thanks bassanclan, I'm sure that would look better. Only concern might be if any water does get into the threshold strip, where can it drain to?

It would work better where no rain can get to the door, which is how it is in my case with a large portico. There are two seals on the threshold strip, so shouldn't get past that, but I have put a couple of small plastic tubes (green) to direct any water outside a bit like a weep vent would work

[Dave Anderson]

I assume the Macclex threshold will have drain holes out the front.  So I think as Russell pointed out the door is sheltered by a porch I can rely on any relatively occassional wind-driven rain emerging onto the stone cill, then running away due to the slope of the cill and paving.  I have therefore removed the drainage channel, allowing me to build up some extra blockwork to provide better support to the stone cill.  I've also filled the cavity with concrete up to top of beam and block, to support the Compacfoam.  

 

Have I missed anything regards damp proofing?  This design really just relies on the DPM wrapping up against the outer skin of blockwork.  I've also removed the DPC under the stone cill, which didn't really seem to be doing anything.  Is this OK?

 

I'm wondering whether I can get the Compacfoam, being lightweight, to sit down tightly onto the DPM.  Or will any creases in the DPM hold it up enabling it to then move under the weight of people on the door threshold?  I'm thinking perhaps I could insert some threaded bars (as indicated on Compacfoam's website) and weigh the Compacfoam down whilst the screed is being poured.

 

Any thoughts appreciated.

Edited June 16 by Dave Anderson
duplicated image insertion

[Dave Jones]

i would ditch the stone cill as it will chip and stain anyway. get a stub cill from the door company then you can run a slim slot ACO tight to it and slab tight as well. You end up with a small 10mm drainage groove which looks much better aesthetically. 

[Dave Anderson]

Thanks Dave, so something like this...

It looks like you'd have a small piece of the stub cill visible below the aluminium?  Maybe a bit messy, but as long as the supplier can colour code it to the door frame it might look OK?  Because we will have cut stone surround to the door I still think it might be neater to use a matching stone cill and just try to keep it clean.  Then just decide whether I need positive drainage in which case just leave a 10mm gap with a channel below as per original post, or rely on the porch to keep the area relatively dry.

Thanks again for your reply.

 

[Dave Jones]

stub cill is same width as the frame so there wont be any sticking out.