Retaining walls can be tricky to build as they need to be strong enough to resist horizontal soil pressure where there are differing ground levels.

One of the things you must get right is the thickness of the wall. It should be at least 215mm thick and bonded or made of two separate brick skins tied together. This should be enough in most cases with minimal water pressure or where the ground level difference is less than a metre.

You also need to consider the effect of ground water, which can create huge pressure on the wall and soak the brickwork if allowed to accumulate behind. Create a way out for the water by adding a gravel trench and pipes through the wall.

If not properly constructed, water can also penetrate the brickwork structure from above through the mortar joints, affecting the long-term durability of the wall. So add brick copings, which must always be F2, S2 (frost-resistant low soluble salts), with an overhang and drip groove to minimise water damage.

Important points

• Don’t forget to include movement joints in the wall and use piers on either side to increase strength at the movement joint position.
• If you’re using two separate brick skins in stretcher bond, you have to provide reinforcement by tying them together. Use stainless steel bed-joint reinforcement every third course to boost the strength.
• Use a high-bond damp proof course below the capping/coping and sandwich the DPC in mortar.
• Waterproof the retaining side of the wall and allow water to drain away from this side through weep holes/pipes.
• Slope paving away from the wall and provide gravel drainage strips where possible.
• Don’t forget to protect waterproofing from damage while you’re building.
• Don’t build higher than one metre without involving a structural engineer

Original Article: http://www.labc.co.uk/news/retaining-wall-basics

This is what happens where there isn’t enough ventilation – the roof covering offers very good waterproofing, preventing rainwater from getting into the building. But it also prevents water vapour inside the building from escaping.

In this case, insulation was fitted between timber rafters, creating an unventilated space between the insulation and the underside of the roof covering. As a result, moist air from within the building has been condensing on the underside of the cold external roof covering.

The problem

• The void isn’t ventilated, which means water vapour and condensation can’t escape and so ends up being absorbed by the timber structure, causing it to rot.

The solution

• When insulating existing roofs, ensure there’s adequate ventilation of the space above the insulation.
• Remember to provide a suitable vapour check layer on the warm side of the insulation.

Remember, whilst insulation will improve the thermal efficiency of the building and result in lower fuel bills for the homeowner, doing it incorrectly can lead to problems such as condensation, mould growth, poor internal air quality and damage to the building structure.

Original Article: http://www.labc.co.uk/news/how-avoid-condensation