weatherproof balcony

kennethmoran

Hello I have precast floors for my dormer bungalow and also have a balcony upstairs above the kitchen. The floors still have to be screeded . Regarding the balcony floor of the bedroom I'm wondering what's the best v way to weather proof it I want to incorporate insulation on it then lay poloythene on top of that . Then thinking of a good concrete mix on top and form a slope to take water of. Any advice would be great thanks

Calahonda52

Is the balcony constructed from the precast floors extending out across the wall?

kennethmoran

yes the gable wall is built on a rsg and precast floor is extended out from that. . I'm going to I think put 100 mil insulation then polythene plastic over that then pour concrete on it . Have to foform a fall off for the rain water.

Calahonda52

Thanks, I am only a beginner here, and am happy to be wrong, but I think you need to think long and hard about the potential thermal bridges here both above and below the insulation layer on the hollow core.
You certainly need to have some sort of a thermal break between the outside sloped concrete slab over the insulation and the over-insulation floor inside.
You then need to think about insulating the underside and sides of the projecting slab as it will act as a massive source of cold back across the RSJ into the room inside, which I presume will have a suspended ceiling, which may not be 100% airtight and being a kitchen below which will produce more than its share of moisture vapour.

You also should fill the cores of the projecting slab with something to stop thermal circulation of the cold air into the rest of the slab.
Do you have MHVR?

This is all do-able now, you just need to tease out the detail before its too late.
What is the RSJ supported, on the inner or outer leaf of the wall or what is the wall make up where the RSJ is supported?

Curious Geroge

I've the same done as OP (although I poured mine so its pretty much sealed). I had a 200mm suspended ceiling and put in 150mm metac under put I was thinking to put 50mm board on the top and trying to sort a slope somehow before finishing with trocal and adding a tile to allow me to walk on it.

I'd be interested to hear how you go.

Safehands

kennethmoran wrote: »

Hello I have precast floors for my dormer bungalow and also have a balcony upstairs above the kitchen. The floors still have to be screeded . Regarding the balcony floor of the bedroom I'm wondering what's the best v way to weather proof it I want to incorporate insulation on it then lay poloythene on top of that . Then thinking of a good concrete mix on top and form a slope to take water of. Any advice would be great thanks

There is a paint on rubber membrane you can use under tiles to waterproof the balcony. It can be dressed up the walls to seal any upstands. I'll pm you the UK supplier's names.

New Build 2015

kennethmoran wrote: »

yes the gable wall is built on a rsg and precast floor is extended out from that. . I'm going to I think put 100 mil insulation then polythene plastic over that then pour concrete on it . Have to foform a fall off for the rain water.

Hi Kenneth,

Have you any update on how you succeeded with this in the end and manage to break the thermal bridge? We have a small balcony/terrace over our kitchen and we are trying to work out the details now without reducing ceiling height much