Threshold confusion

[Selfbuildsarah]

Our door and timber frame companies are now asking for details on thresholds for our build. We are struggling with this as we have no build knowledge. Using this forum and AI hasn’t clarified things. Would appreciate some guidance please. 
 

Information needed from the door company:  

• Finished Floor Level: for each opening that extends down to floor level, a dimension or datum indicating the top of the final floor covering is required.  
• External wall finish: details required includes dimensions of any additional build-up such as cladding, render, insulation, etc. 
• External reveal depth: including the external wall finish. This is needed to calculate your sill depth 

 

 If you are planning to build upstands, screed or carry out other similar works, please take into consideration the height of your door thresholds and/or sill with your required threshold finish. N.B. In addition to the threshold, doors can have a 25mm high box section sill that also needs to be installed below Finished Floor Level. Carrying out works without calculating any requirements to bury door thresholds and/or sills may prevent the opportunity of achieving a flush threshold, and further building work may be required.”

 

Our timber frame company (MBC) want to know what recesses we need in the foundation

They are working on construction drawings at the moment. (Insulated slab with ufh)

Is there a sensible, logical thought process for all this? Do we really need to be thinking about what floor coverings we are having at this stage when we haven’t even got construction drawings?

One of our problems is we haven’t had an architect on board. We had a Potton design and we’re ready to proceed just as they withdrew from the market.

 

Apologies for long post!

[Mr Punter]

You need someone to do the detail drawings.  This would normally be your architect.  Can MBC suggest?

[Selfbuildsarah]

Thank you.

We have found one to do our building control once we have plans. We don’t have any detailed drawings from Potton (that was our next move before we found out that they were pulling out). MBC are currently converting our original Potton design drawing. Trouble is, it’s all a bit chicken and egg. MBC are asking for threshold details. Architect wants plans from MBC. 

[Russell griffiths]

Your door supplier should give you a threshold drawing, send this to MBC, you need your floor finish decided, will you be using the MBC slab, they should take it from there. 
 

you have hit the jackpot losing potton and going MBC. 

[Dunc]

I'd expect the architect to sort the threshold and FFL.

Ideally you'd decide what your floor covering is likely to be so that the architect can make appropriate allowance. eg. ours allowed 22mm for porcelain tiles (+ grout & mat). If you were planning LVT maybe you'd need a lot less. If you don't know yet, best to be conservative (larger allowance) and make it up in screed later if needed.

 

Given your fairly unique situation I'd have thought MBC could generate something generic and allow the architect to sort out the detail before coming back to a second iteration. However, I don't understand how you can have construcion drawings without all the details from someone (usually the architect) that will affect the construction, e.g. where waste pipe runs are (need this for the foundation as a minimum), where you might need to run MVHR ducts (can affect structural members in floors/roofs), what your external cladding is, roof covering, etc etc.

[Selfbuildsarah]

7 hours ago, Dunc said:

I'd expect the architect to sort the threshold and FFL.

Ideally you'd decide what your floor covering is likely to be so that the architect can make appropriate allowance. eg. ours allowed 22mm for porcelain tiles (+ grout & mat). If you were planning LVT maybe you'd need a lot less. If you don't know yet, best to be conservative (larger allowance) and make it up in screed later if needed.

 

Given your fairly unique situation I'd have thought MBC could generate something generic and allow the architect to sort out the detail before coming back to a second iteration. However, I don't understand how you can have construcion drawings without all the details from someone (usually the architect) that will affect the construction, e.g. where waste pipe runs are (need this for the foundation as a minimum), where you might need to run MVHR ducts (can affect structural members in floors/roofs), what your external cladding is, roof covering, etc etc.

 

MBC have asked us where we want waste pipe runs etc and MVHR ducts (we have someone lined up to do this but of course he needs plans too!) As you said, if they can come up with a basic drawing to get started with the architect we can move things forward. To add another complication we have a balcony to consider!

[Selfbuildsarah]

7 hours ago, Russell griffiths said:

Your door supplier should give you a threshold drawing, send this to MBC, you need your floor finish decided, will you be using the MBC slab, they should take it from there. 
 

you have hit the jackpot losing potton and going MBC. 

I will go back to the door supplier and hope they can do that. Yes, insulated slab.

Thanks for your reassuring comment re MBC! It all feels a bit of a muddle at the moment because we haven’t followed the usual route starting with an architect. 

[Nickfromwales]

6 hours ago, Selfbuildsarah said:

 

MBC have asked us where we want waste pipe runs etc and MVHR ducts (we have someone lined up to do this but of course he needs plans too!) As you said, if they can come up with a basic drawing to get started with the architect we can move things forward. To add another complication we have a balcony to consider!

The parapet is easy to (re)detail, just from previous experience I noted that MBC give a rudimentary timber detail which imo could be better if it was insulated more robustly in the early design phase.
 

I’m doing revisits of these kinds of things for a sizeable MBC client atm, and it’s surprising how the basics are great but there are still quite a few gaps to fill / simple improvements we’ve made for finite detailing. I guess some are more based on personal preference too, to be fair, but some are more architectural faux-pas which until I (and the newly appointed AT) highlighted them the client was oblivious to them.

 

Recesses in the slab etc are easy once you have a detailed drawing from the window supplier, but even Norrsken got their structural openings wrong (typos); which I had to highlight after measuring up and spotting the error. The gotcha is not conveying this info early on to your BCO eg if you want raised external floor levels to keep the floors flush (or near as damnit) outside > in, as you need to ask for a deviation from keeping the knee jerk 150mm splash below the external rain screen to losing it to raise the grade to suit level threshold / floors.

 

I’ve had MBC move a steel, to sympathise with M&E pathways, plus to make the corridor into the kids rooms wider, which MBC did without hesitation.

 

Great company to work with so yes, you’ve landed on your feet there afaic.

 

Potton are more ‘rubber stamp’ imho, and do little for a good foundation / high-performance house marriage….may be better these days but I wasn’t impressed when one of their previous clients approached me and the list of issues began to grow. Was difficult to stick my nose in and make fundamental changes and speak to particular people who would / could make this happen. Way more fluid with MBC, and so far nothing has been refused or pushed back.