Advise on type of works for mezzanine

[hotnuts21]

Hello, as part of ongoing extension/refurbishment of the house, we are considering opening up the bedroom ceiling into the loft and having a mezzanine style opening level above an ensuite at the end of the bedroom. We would then look at putting in one of those velux rooflight balconies.

However this is still very much at the planning stage, and before we get as far as paying for structural engineers etc, I would like to get an idea of the type of works that might be required and if our roof lends itself to this type of work without a lot of alteration.

The house is a 1907 Edwardian terrace, There are 4 wooden beams running the length of the roof, which hold up the rafters. The roof does appear in the bedroom below, so I know the 'floor' of the mezzanine would be lower than the existing ceiling. The wooden beams run from a brick wall at either end and are supported about a third of the way across with an a frame of sorts. This would not be in the area we would open up, it appears to be over the wall between the two front bedrooms.  As always a picture is better than words so I have added some photos to explain.

Mezzanine area marked with green box, A frame marked in orange. 

This is just to get an idea of feasability at this stage so any and all opinions excepted.

[Temp]

OK so first thing is to make a scale section drawing like you have to show what the headroom is going to be like.

 

The four beams are called Purlins. Sorry if obvious but they can't easily be removed and you shouldn't cut or modify them or any posts under them without input from an SE or similar.

 

You will need insulation  at rafter level. The roof make up should be something like...

 

Tiles

Battens

50mm void (ideally ventilated at eaves and ridge but if you have lots of gaps between tiles and no membrane you might get away without ridge vents. Discuss with BCO) 

200mm PIR insulation (gaps to inside sealed with expanding foam but don't block ventilation above the insulation)

Vapour barrier 

Plasterboard 10mm

 

The thickness of the mezzanine floor will depend on the joist span. There are joist span tables on the web. At 3.5m span ? you should be ok with 170mm deep joists. Add 18mm floor on top 10mm for plasterboard on the bottom so total around 200mm.

 

Make a scale drawing and see if the headroom is ok. 

 

It might be possible to install an ordinary velux roof light between two purlins but more dimensions needed. I think the balcony style are likely to need at least one purlin cut that is structurally more difficult unless there happens to be a load bearing wall below where the cut is needed. Balcony type may also need Planning Permission.

 

I think I would make your own scale drawing first to check headroom. Then see if you can find an SE to come take a look and if he thinks its feasible have him quote to produce drawings for Building Control Approval. If planning permission is required first for the balcony velux he might be able to recommend someone to do those drawings for you.

 

I might be misunderstanding your drawings but it looks like any velux over the bathroom will be near the verge of the roof. That might be an issue? You might need to allow one rafter Bay before you insert a velux otherwise tiling is an issue? Edit: Actually it looks like its near the party wall so might be ok.

Edited July 14, 2021 by Temp

[hotnuts21]

Hi Temp,

Sorry for taking so long to come back to you and for the detailed answer.

Yes I think we will need to cut the purlin to do the work and It was around this and supporting the new floor where my concerns were. Im trying to get a feel for what work would be required if we do this before I speak to a SE. I dont want to shell out hundreds just to find out its impossible or way out of realistic budget, but it might be the only way forward. 

 

Thanks again, all the other points I had already considered and we think its a possible go, but I want to find out more before pulling the trigger ?

 

Paul