Damp Issues in Victorian House

[BK21]

We purchased a sandstone house built 1891, which is suffering from damp issues. We knew works were needed but are now discovering that the house was poorly maintained for quite a while. The house has a rear extension which is original and is lower than the rest of the house (no subfloor), and the floor has been concreted over at some point. When renovating the kitchen we discovered the roof was badly leaking for quite a while causing damp on the internal wall, we thought this was repaired but have had further signs of damp on the new plaster behind the lower kitchen cabinets so are investigating other reasons. There are a number of external issues but I think the main issue is the external ground level has been raised too high? For context we are on a hill so the slope run towards the house, our floor level in the main part of the house is around 1ft higher than DPC, cannot see DPC on extension. The previous owners had covered a drain with soil and a plant which has now been cleared to reduce the surface water build up. The gutters are also very corroded which I think is a contributing factor, new ones are being installed this month. Looking for advice on a few things :

Can surface water cause rising damp an internal brick wall or any other possible causes?
Would installing channel drains around the rear of the property help with ensuring no surface water sits against the foundations?
Is the green on the stone being caused by moisture from ground level?
How much lower should the ground level be to the DPC?
With the damage to stone, can this be easily repaired?

I have never used lime mortar or repointed/rendered but fairly confident in internal building/DIY jobs and hopefully save some money doing the job ourselves.

 

[alexander]

any water can cause dampness surface water being no different to other types of water although rising damp is mostly caused by cement/concrete. drainage maybe an advantage to redirect the water away from the property although it looks like the water level might be quite high in your area so it would be case of were you could redirect this,
the green on the stone is not being caused by moisture from the ground, its most probably being caused by moisture held in the stone work by the cement pointing that's been carried out previously, you can see the stone work decaying around the cement work as the cement is a lot stronger than the stone work causing the stone to decay a lot faster than the pointing should have been a lime mortar used for repairs.
the ground level should be at least 150mm below the damp proof course.
good luck Alex

 

[Cubist]

See below.

• Can surface water cause rising damp an internal brick wall or any other possible causes?
  • Yes. Surface water and/or ground water can contribute to damp rising through the foundations and any underground brick or stone-work to appear in the walls above ground.
  • The term 'surface water' typically refers only to visible water rather than that typically held among the rocks and soil.
• Would installing channel drains around the rear of the property help with ensuring no surface water sits against the foundations?
  • No, ACO type drains are typically installed with their upper face level with the surrounding ground. As the bottom of these is often less than 150mm below the surface of the ground they cannot handle any water found below that level.
  • A French Drain, or a Zebcolm Trench, would be better suited to your needs and these should be installed on the up-slope elevation of the house and its down slope sides to channel surface water away from the property.
• Is the green on the stone being caused by moisture from ground level?
  • Yes and No - Sandstone is perhaps the most porous stone and will absorb water moisture from any available source.
  • As well as such moisture the algal blooms you are seeing on the lower sections of your wall also depend on being shaded from strong sunlight and sheltered from air movement.
• How much lower should the ground level be to the DPC?
  • Circa 150-200mm but, as yours is a stone built structure the cue for this measure should be taken from the thickness of the stones near the foot of the building.
• With the damage to stone, can this be easily repaired?
  • Some may disagree with me but;
    • Repairs to the surfaces of those stones would be difficult, costly and probably very expensive whilst also proving unsightly and unattractive.
    • Repairs to cracks and fissures in individual stones may be possible but expert advice would be needed.

 

[BK21]

Thanks for the reply guys. Initially we had surface water pooling next to the exterior wall. I’d started trying to dig a channel to divert it away from the house which is when we discovered the drain had been blocked, hoping that this being cleared considerably helps the damp. I have seen a few posts about French drains so will definitely look into doing this when we lower the ground level.
We are going to get someone to repoint the whole house at some point but from what I’ve seen this can cost a few thousand, most of the damaged stone is at the rear so hopefully we can repair it with lime mortar to prevent further damage until then.