building against non-DPC wall

[sm_jamieson]

I have to build a new wall at right angles to an existing wall that does not have a DPC. The existing wall is a 9 inch party wall that, where the new wall abuts, forms part of an outside toilet. The wall does have 2 rows of blue bricks that may for a rudimentary DPC I suppose - but I don't think there is a slate DPC in there. The new wall to be built against this is the outside skin of a new cavity wall. Since there is nowhere really to lap the new DPC into, what should be done at the join with the old wall? The wall as a whole is to be tied in using a wall starter kit, but the instructions say do not use this below DPC, I guess because as a general rule this would then be bridging a DPC. I could run the DPC vertically at the interface, but then the below-DPC part would not be tied to the old wall at all. What would usually be done in such a situation ? Thanks, Simon.

[Phil]

The blue bricks will be engineering bricks, an effective DPC. run the new DPC vertical for a short distance. Tooth in or use ties below DPC if needed.

Phil.

[sm_jamieson]

Thanks, makes sense to me. Assuming you mean run it vertically upwards ! Simon.

[mail]

Simon Be aware that damp rises in the mortar as well as the bricks and no matter how blue and impervious they are they are prone to dampness rising in the only continuous connecting element - the mortar. That having been said because the bricks are not conducting - rising damp is less prevalent in such structures and significantly so - it is just that the bricks are not a "complete" dpc as often is thought.

Chris

[sm_jamieson]

Yes I agree. I believe one reason why a strong cement mix was recommended in the DPC was to make it more waterproof as well as stronger. Of course the cement may crack, so too strong a mix is counter productive. My house (1930s, solid walls) uses strong cement mortar in the 2 blue brick courses (it does also have slate DPC in the main house walls), then lime mortar for the rest of the house. Seemed stange to me. Houses in my area were built in a traditional style quite late on apparently. At least with solid walls I don't have to worry about cavity trays when building an addition at the back of the house ! Simon.