Hi,
I am in the midst of building our new home in France and would like, for obvious reasons to install a DPC.
The building is quite different to an average UK building (but standard for over here) so I am having a hard time finding information on, determining the correct type and method of installing a DPC.
In France the average DPC is either non existant or a simple screed with a waterproofing admix. When I ask about the bitumen/plastic roll type dpc over here, which does exist by the way, I get some strange looks and virtually everyone trys to talk me out of the idea for reasons like "it creates a fracture in the upper and lower half of the building, the building will not be as solid" etc.
The french regs do state that either -
1/ The concrete lower floor extend fully out through the whole width of the wall or if this is not the case (as in my building) that either a mortar/waterproofing admix screen is run along the whole length of each wall. The bottom of the floor should be a minimum of 5cm above the finished exterior ground level.
2/ A bitumen/pvc/plastic type dpc can be used sandwiched between two beds of mortar at a height of at least 15cm above the exterior ground level.
There you go then I here you say! Well here is my problem.
I would prefer to not do the screed method because firstly I am not particularly confident that it will act as a good dpc for the life of the building and secondly most so called builders only do this method over here for the simple reason theat the walls are not level! Mine obviously are.
The type of structure that I am building is used in approx 80% of new build over here now and consists of a strip foundation and a single bearing wall (no cavity over here) normally built with concrete breeze blocks (20x50x20cm) at various heights but in my case is the standard 60cm/3 course. This wall is has vertical rrebar reinforcement at the corners and every 5m in long runs, tied into the foundation reinforcement.
The plumbing, drainage, elec supploes are run inside this "crawl space" then into the house.
The exterior ground level with be 40cm up this wall so the dpc would need to be on top of the 3rd course.
The ground floor is a block and beam type floor which consists of dry laid pre stressed concrete beams laid across the walls, interlocking insulation polystyrene panels (were required), otherwise osb/plastic panels, steel reinforcement rebar around each length of wall tied into the vertical reinforcements in the wall (at corners and every 5m approx), steel reinforcement mesh panels across the whole surface and a slim approx 5cm thick/20cm high brick is laid around the perimeter which acts as shuttering for the concrete compression screed on the top. Might sound complicated but isn't really.
So my thought regarding the dpc -
it has to be at 15cm or above the finished exterior ground level which puts it directly on top of the wall before the block and beam floor.
In needs to be under this floor really anyway to stop any moisture entering the floor and walls (in this type of stucture ober here a DPM is not used as the floor is supended).
As the beams are laid dry (only on the inner edge of the wall, approx 7cm) and are quite heavy I would think that a mortar bed under the DPC is pointless ? (The wall top is quite smooth, no frogs but the blocks do have thub holes in for lifting).
Can the dpc in this case be laid dry do you think?, could there be any problems with this (remember there are 14x14cm concrete vertical reinforced sections in the wall at every corner and every 5m on the longer straight spans, extending from the concrete foundation to the top of the wall).
Yes I realise that the dpc would have to have small holes cut out for the rebar to extend through which sort of defeats the object but must be better than nothing and think that damp has a hard time creeping up through concrete
My real problem (if a problem at all) is the "shutter block) which is approx 5cm thick but has a wide lower portion. This is laid using mortar around the perimeter as I have said and acts as shuttering for the screed. The main problem is - Will this hold ontop of the dry laid dpc??especially while the concrete is being poured? Obviously after the concrete has set there will be no problem at all.
Do you think it would a good idea in this case to apply a bitumen primer to the wall top and torch bond the dpc (obviously a bitumen based dpc) to the wall. (Visqueen zeedex high bond?).
Wow, sorry a bit of a long post!
Let me know your thoughts please. Can post photos if needed.
Cheers, Matt
I am in the midst of building our new home in France and would like, for obvious reasons to install a DPC.
The building is quite different to an average UK building (but standard for over here) so I am having a hard time finding information on, determining the correct type and method of installing a DPC.
In France the average DPC is either non existant or a simple screed with a waterproofing admix. When I ask about the bitumen/plastic roll type dpc over here, which does exist by the way, I get some strange looks and virtually everyone trys to talk me out of the idea for reasons like "it creates a fracture in the upper and lower half of the building, the building will not be as solid" etc.
The french regs do state that either -
1/ The concrete lower floor extend fully out through the whole width of the wall or if this is not the case (as in my building) that either a mortar/waterproofing admix screen is run along the whole length of each wall. The bottom of the floor should be a minimum of 5cm above the finished exterior ground level.
2/ A bitumen/pvc/plastic type dpc can be used sandwiched between two beds of mortar at a height of at least 15cm above the exterior ground level.
There you go then I here you say! Well here is my problem.
I would prefer to not do the screed method because firstly I am not particularly confident that it will act as a good dpc for the life of the building and secondly most so called builders only do this method over here for the simple reason theat the walls are not level! Mine obviously are.
The type of structure that I am building is used in approx 80% of new build over here now and consists of a strip foundation and a single bearing wall (no cavity over here) normally built with concrete breeze blocks (20x50x20cm) at various heights but in my case is the standard 60cm/3 course. This wall is has vertical rrebar reinforcement at the corners and every 5m in long runs, tied into the foundation reinforcement.
The plumbing, drainage, elec supploes are run inside this "crawl space" then into the house.
The exterior ground level with be 40cm up this wall so the dpc would need to be on top of the 3rd course.
The ground floor is a block and beam type floor which consists of dry laid pre stressed concrete beams laid across the walls, interlocking insulation polystyrene panels (were required), otherwise osb/plastic panels, steel reinforcement rebar around each length of wall tied into the vertical reinforcements in the wall (at corners and every 5m approx), steel reinforcement mesh panels across the whole surface and a slim approx 5cm thick/20cm high brick is laid around the perimeter which acts as shuttering for the concrete compression screed on the top. Might sound complicated but isn't really.
So my thought regarding the dpc -
it has to be at 15cm or above the finished exterior ground level which puts it directly on top of the wall before the block and beam floor.
In needs to be under this floor really anyway to stop any moisture entering the floor and walls (in this type of stucture ober here a DPM is not used as the floor is supended).
As the beams are laid dry (only on the inner edge of the wall, approx 7cm) and are quite heavy I would think that a mortar bed under the DPC is pointless ? (The wall top is quite smooth, no frogs but the blocks do have thub holes in for lifting).
Can the dpc in this case be laid dry do you think?, could there be any problems with this (remember there are 14x14cm concrete vertical reinforced sections in the wall at every corner and every 5m on the longer straight spans, extending from the concrete foundation to the top of the wall).
Yes I realise that the dpc would have to have small holes cut out for the rebar to extend through which sort of defeats the object but must be better than nothing and think that damp has a hard time creeping up through concrete
My real problem (if a problem at all) is the "shutter block) which is approx 5cm thick but has a wide lower portion. This is laid using mortar around the perimeter as I have said and acts as shuttering for the screed. The main problem is - Will this hold ontop of the dry laid dpc??especially while the concrete is being poured? Obviously after the concrete has set there will be no problem at all.
Do you think it would a good idea in this case to apply a bitumen primer to the wall top and torch bond the dpc (obviously a bitumen based dpc) to the wall. (Visqueen zeedex high bond?).
Wow, sorry a bit of a long post!
Let me know your thoughts please. Can post photos if needed.
Cheers, Matt
Last edited:
