DIY build vertical damp questions

GreatOaktree

Hi all,

Myself and my girlfriend bought an old stone house with no bath room and no septic tank. The planning for the septic tank had just ran out when we bought the house. I started to build on a bath room last summer and have the footings done. I poured the foundations by hand, laid the DPC and have the footing wall finished.
My questions are what do I do next to prevent vertical damp rising through the floor ?
Do I lay a vapour barrier now ? Do I tape it to the DPC ? Should the vapour barrier cover the footings ? Is a radon barrier essential ?

jack of all

You should get a copy of the Homebond builders manual to help you out on the traditional details- your local public library should have it on their shelves, if not you should be able to pick up an older edition (maybe a little out-dated but fine for the basics) for cheap. You need to consider radon/ DPM, wall DPC height above ground level, floor insul etc. Too much detail to go into here unless you research the basics first and see some detail drawings to understand how it all goes together.

GreatOaktree

Thanks Jack of all much appreciated
I've spent time labouring and ran in straight walls (10 years ago when I was 18) but this is the first time I've started from scratch on my own. I'll go looking for the book today.

jack of all

If you have the practical skills then I think the book would be a very good and cheap investment, save you making any costly mistakes when it comes to the build.

GreatOaktree

Thanks jack of all,

I was lucky enough to find the book in the library. I'm still a little confused. If I infill the floor with gravel from the bare earth up to the height of the footings and then lay a DPM over the floor area and footing wall then wont the damp be fit to rise up through the gravel and horizontally into the footing wall ?

So should the DPM be laid on the bare earth before the gravel layer and up the inside of footing wall and over the top ??

jack of all

Any chance you could stick up a pic or two of what you have built at the moment. I don't want to confuse matters further by giving you bad advice and I want to ensure that I'm on the same wavelength as you regarding terminology- the footing you refer to I take to be the rising walls, constructed in concrete blockwork, with or without a cavity?

Typical floor construction would consist of 150mm concrete on 500 gauge dpm/ slip layer (to prevent water and fines from concrete draining down into the insulation and any voids below), on rigid floor insulation (thickness will depend on U-value required, size of slab, perimeter exposure etc- put in the thickest, highest performing product you can afford), on 1200 gauge DPM or radon barrier, on blinded, well compacted hardcore (typically 200mm deep overall, 804 clean crushed stone). The Homebond manual will detail perimeter insulation, wall dpc and overlap etc.

GreatOaktree

Sorry no pic, I'm actually embarrassed to show you what I've done so far. I had originally planned to construct using cobb so the foundation trench is near 3 foot wide. The DPC is 2foot wide and the rising wall is solid with no cavity. There is only less than 1 inch of DPC exposed on either side of the wall.

So at this stage I should lay the DPM onto the bare earth and over the rising wall ??
Then lay aggregate and wack that in place to obtain a level surface, then the floor insulation topped off with 150 mm concrete.
I've no planning and wont be applying for any as it falls wit regs of not needing any.

Thanks for taking an interest jack

jack of all

Starting from ground up:

Remove top soil 150- 250mm below finished ground/ path level. Take out any soft spots, make up level with crushed stone.

Place crushed stone/ hardcore 150-200mm deep approx, compact well, blind with sand or quarry dust.

Place DPM(1200 gauge or radon barrier) over the entire slab area, turn up at perimeter upstands and over rising walls.

Place perimeter insulation and floor insulation, place 500 gauge slip layer/ DPM over.

Pour concrete slab, screed or powerfloat as required.

Roll out wall DPCs over floor DPM where it overlaps rising walls.

(Rising walls should include a small cavity below wall DPC level to allow water which enters the walls to drain down into the ground and not back into the building)

Start your external walls.

Study the Homebond manual, it's a basic reference point for any students studying construction technology nowadays AFAIK, and you won't go wrong.

GreatOaktree

Thanks Jack it's all much clearer now. Thats great info.
I'm feeling much more confident about it.
Thanks again.