Cavity Wall Insulation Bridging DPC?

[thesquiff]

Just had a British Gas Energy Survey done and they reckon cavity wall insulation wouldn't be a good idea as there is not enough clearance between ground level and our damp proof course. We could get rising damp in the walls due to bridging of the damp proof course.

What I am unsure of is how does this change if there is greater clearance between ground level and the DPC? Surely the cavity will fill up just the same and bridge the DPC? I'm confused.

 

[EFLImpudence]

Did they propose fitting the insulation outside?

No such thing as rising damp.

 

[thesquiff]

Having thought about it some more I'm guessing that he must have been concerned that heavy rain could splash over the top of the DPC and bridging through the insulation could make the internal wall damp. That's the only way I can think of it being a problem.

He may not have used the term "rising damp" - I probably made that up.

I guess if the DPC was higher off the ground then there would be less risk bricks above the DPC getting damp.

 

[EFLImpudence]

That makes more sense but I don't think bricks (is it bricks?) are that porous.

After all they get wet with driving rain all the way up.

 

[conny]

DPC membrane should be at least 6", (150mm), above solid ground level to prevent 'splash back' on the bricks above.
(If the ground is soil/earth then a channel should be dug and filled with loose gravel to prevent this splash back happening.)

Bricks are porous but will absorb a lot of moisture before becoming saturated. That said, bricks below the dpc do absorb water from the base of the building, be it concrete foundations or whatever. These are more susceptible to crumbling over a long period of time.

I was always under the impression cavity insulation was impermeable anyway so would actually act as a barrier to outside moisture migrating across to inner walls.

 

[Alastairreid]

Surely the cavity will fill up just the same and bridge the DPC? I'm confused.

Here is an interesting read from a guy who knows his stuff.

http://www.askjeff.co.uk/cavity-wall-fill/