Renovation damp

From Sustainable Building Resource

Damp

Damp is caused by condensation or from water ingress.

Condensation can be caused by a number of issues including:

Thermal bridging

Poor ventilation

Inadequate heating

Inadequate insulation

Water ingress can be from:

Rising damp (Note that 'Rising Damp' rarely, if ever occurs and injection damp proofing does NOT work - it simply destroys multiple courses of brickwork with useless holes. Every case of so called rising damp can be explained by a combination of the other issues discussed here on this page)

Broken or inefficient roof hardware - leaking gutters, downpipes etc causing excessive water splash on walls

Leaks

Structural issues

Damp leads to a number of health and well being issues and so needs to be dealt with.

Solving damp is one of the most important tasks for any renovator, but sometimes well-intended improvements can inadvertently create new damp problems. Here are some of the common causes:

Raising external ground levels above the dampproof course (DPC), or above floor level, leading to penetrating damp.

Painting the exterior of a solid-walled building (no clear cavity) with impermeable waterproof paints or sealants—leading to penetrating damp.

Rendering or plastering the internal walls with impermeable gypsum based plasters - only lime plasters should be used, and only permeable paints (limewash, or Beek - Insil type silica based paints)

Adding double glazing and blocking fireplaces, flues and vents without compensating with adequate alternative ventilation — leading to condensation problems.

Sloping new paths towards rather than away from the building—leading to penetrating damp.

Making new additions, such as a conservatory or extension, without fitting flashings, cavity trays, or other suitable means to divert any damp away from the building.

Using hard cement fillets as a weatherproofing measure in valleys, abutments or at the base if chimneys — it will crack, and damp will be able to get in. Use lead flashings, valleys and skirt/apron.

Sealing the roof structure with new felt or spray-on urethane insulation without ensuring the timbers are adequately ventilated.

Using hard cement render mixes on the exteriors, as they will eventually crack and draw in penetrating damp through capillary action.

Pouring a new concrete floor in place of a suspended timber floor without adding adequate damp-proofing measures, both horizontally and vertically, and compensating for the loss of subfloor vents.