Keeping damp out of the loft

A bit more advice please you guys.  

When I construct a new loft, I normally put down breeze blocks at each corner and make sure they are square and level, then I put in more along the sides and some in the middle to make the centre of the loft sturdy.

Then on top of that I lay down a foundation of wooden timbers around about 4 - 4 1/2 inches, or around 100-110 mm, square, with corresponding timbers in the centres, giving the whole construction a very firm base.

On top of that I lay the floor, which is always WBP or marine ply, between 15 - 18 mm thick, and screw those down to the floor joists.  Before laying the floor boards, we always paint the underside with at least 2 coats of sealer or wood preservative, and paint the top side with 2 or 3 layers of yacht varnish.

Then I make framework panels, normally out of something like 2 1/2 x 3 inches, or 60 x 80 mm.  Then attach either plywood sheets or tongue and groove to the framework, and hoist them in the air, normally beginning with a back section and a side section screwed together to make a corner, to make a rigid base to work from.

I always make sure that the external timbers, whether that is ply or tongue and groove or shiplap, go down beyond the floorboard level and down over the floor joists, but still sometimes, when it rains heavily, I get an ingress of water which seems to be coming upwards from the end of the exterior boards.

Should I put in some kind of water barrier, Visquene, damp course etc?  and if so, where?  between the breeze blocks and the floor joists, or between the floor joists and the floor boards?

If I should put in some kind of damp course, what exactly should I use?  I have some visquene but it is about 10 years old.  If I have to buy new, that's OK but I need to know exactly what I should buy.

Over to your expertise!

Phil

you could put dpc on top of the blocks before you put the floor joist on phil, I never have and ive never had a problem....but you could do.

also If using tounge and groove I would make sure each piece is firmly tapped into the other pieces, I use a rubber hammer......also on the outside of each sections when fixed together put a lat down where the framework is exposed.

also when painting / staining make sure you paint the edges that overlap the floor or damp could creep in.

on our last loft erected 2 year ago now we had a hardcore base to work from and laid block piers 3 blocks high and then a timber frame on top of that out of fence posts then with a staple gun tacked a 150 mil dpc to the fence post frame and have had no problems ...make sure the piers and frame are under the loft far enough so that any water running off the loft does not hit them and I am sure you will be ok atb

What is DPC and how does it come?

Phil

blueskylofts wrote:

What is DPC and how does it come?

Phil

dpc phil, is damp proof course....it comes on 4 1/2 wide or 9 inch wide rolls, its the damp course for brickwork, but is ideal for putting under the floor joists.