RSJ &Thermal Bridging - Proposed Build

[Nik Nak]

Hello

 

I know this topic has already been extensively covered on the forum but there is however a slight variation which  i am looking for a solution please.I have spoken to two builders who cannot provide a suitable explantation.

 

Overview

Proposed new build extension (drawing below) with 3600mm x 2100mm opening to accommodate bi-fold doors. I have been advised to have a rsj installed above the doors due to weight of roof design.

 

450mm thick wall construction details as follows (photograph below) 

Outer     150mm facing in natural stone

               100mm block

                50mm void

                50mm insulation

                100mm block

 

The drawing (below) is from an architect.He has not provided a drawing where to position an rsj above the intended bi-fold door. Speaking to a couple of builders they suggest a wide steel plate be welded to a rsj in order to achieve the required width .

My questions are

- Although feasible - this would not stop thermal bridging? 

- Where would the bi fold doors sit in relation to the stone / block work - would this also be an issue?

 

Any advise or comments would be appreciated. Thank you very much for any assistance

 

 

[Mr Punter]

It is a question for your architect and engineer as the steel needs to support all that stonework and blocks and needs adequate bearing either end. You could use a separate steel for the inner leaf. Also I would ask them why you only have 50mm of wall  insulation, especially as your wall is 450mm thick.

[Gone West]

Hi, welcome to the forum. I'm trying to understand the makeup of your wall. Why do you have two 100mm block walls as well as a 150mm stone wall. Why not use stone slips on the outer block skin and increase the amount of insulation to stay within the 450mm. Alternatively use the 150mm stone wall as the outer skin and remove the attached block wall and again increase the insulation?

[Declan52]

You can use a welded piece like what you propose.  But it's a big lump of steel so will be a thermal bridge but with twice as much insulation going in the floor than what you are putting in the cavity that detail ain't your biggest issue. 50mm is a long way from what you hope will lead to  a warm room. 

As above you could use 2 skin of blocks and increase the cavity to 150mm min and use a stone cladding type product.  I used one on mine and it's real stone but only 25mm thick so won't need extra width in your founds or the extra steel.  Comes with corners so looks more realistic. Two 4m concrete prestressed heads will easily do that opening.  With the money saved on your founds and the steel you can put more insulation in the cavity and have a room that won't require the heating on all the time.  

 

This is a video of how it goes on.  There are plenty of different companies that do this type of product now. 

 

[Nik Nak]

Firstly, thank you all for your responses.

 

The drawings you see were provided by an architect on A3 size paper and the hand drawn diagram is when I asked for further detail.

 

The foundation has already been laid  at 450mm where the stonework is going - 

The idea of the stone addition was for cosmetic appearance purposes - although judging by some of the comments maybe I should increase the insulation and do away with the stonework and perhaps just render? Although don’t really want to go through planning again...

 

Unforunately I cannot get a drawing from the architect to show the build up above the proposed rsj.Either way it looks as though the general consensus amongst the responses is that I should increase the insulation to i. e 100mm ?

 

Do you think I could make the wall the same thickness as the rest of the build and either just render or use a stone slip for cosmetic purposes ? If I do it this way then will the 50mm insulation on his sketch be adequate enough ?

 

At least this should solve the problem with the initial rsj problem to  450mm thick wall.

 

Any further thoughts or comments would be appreciated. Has been a bit of a nightmare dealing with drawings showing minimal detail.

 

 

Thank you all again

 

 

 

[Declan52]

No matter what you have on the outside,  stone or stone slips or render 50mm insulation just isn't enough. 

If you have it built to suit 450mm then you have 200mm of a cavity to play with.  If it was me I would fill all 200mm with insulation and use stone slips.  

Means you don't have to worry about a steel rsj,  a standard concrete prestressed head will do.  I have a 3.6m opening that was originally for bi folds before we looked into them and found out how many issues they can have, please say you have done your research on them, and I have used 4.2m heads for mine. 

You will end up with it looking exactly how you want,  clad in what ever choice of stone but it will be much much nicer to sit in during days like these.  You don't need a stone mason to put slips on either,  a tiler or a brickie should be able to do it.  You can ask the rep of the slip company to give you details of a few guys he knows that do this type of work.