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Raised external ground levels will cause internal dampness

November 12, 2010

There are very few guarantees in life. There are no job guarantees, no pension guarantees and certainly NO damp guarantees!

However, I can guarantee one thing. If you raise the external ground level adjacent a solid brick wall, you’ll get internal dampness!

Observations

The patio is higher than the internal floor level by 75mm!

Penetrating dampness due to patio level

A recent inspection of a house with a solid brick wall highlighted the importance of keeping external ground levels as low as possible, relative to the internal floor. 

The dampness internally ran right along the base of the wall and there were also signs of condensation mould.

However, upon further investigation, I noted that the internal floor level was actually 75mm BELOW the external ground level. Moreover, the DPC had been positioned above the external ground level by another course of bricks!

The problem

Ground levels are often raised when a new patio is laid. The mistake people make is not to remove enough of the existing ground to ensure the FINISHED height of the new patio is at least 15cm (2 courses of bricks) below the internal floor level.

The cost of a large skip and additional man hours is required to remove the old paved area and sub soil to the correct depth. This cost needs to be ADDED to the cost of the new patio.

Solution

One method of ensuring the old paving and sub soil is removed BEFORE the new patio is installed, is to split the work up into two packages.

 The 1st half of the work includes digging out and carting away the old paving to the correct depth, while the 2nd half will include laying the new patio to the correct height. Payment should be split accordingly, perhaps 25% for the 1st half and the rest upon completion.

NB  Make sure you pay for the skip and not the paving contractor, they’ll hire a tiny skip!

Recommendations

1. When estimating the cost of a new patio, add on the cost of digging out the old ground to the correct depth and the cost of a large skip.

2. When laying a new patio, ensure the FINISHED patio height is at least 15cm below the internal floor level and never partially cover up air bricks.

3. Ensure that the new patio slopes away from the brick wall, to allow any surface water to drain away from the house and perhaps into a flower bed or a nearby gulley.

4. Don’t run the patio right up to the masonry wall. Leave a 10cm trench and fill it with large stones about 2.5cm in diameter to prevent damp soil from touching the brickwork.

P.S –  Back to damp guarantees…

If you think you’ve got a damp guarantee from a remedial damp company, I would suggested you have another read! The guarantee will probably be a materials and workmanship guarantee for the remedial treatment and not a performance guarantee for the alleged dampness. Sorry!

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From → 3. Dampness

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