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Ventilation of Timber-Framed Structures

Ventilation of the external walls of timber-framed construction is necessary so as not to allow moisture build up in the cavity which may cause decay to the structural timbers. External walls of a timber-framed dwelling are normally comprised of a number of layers which can be seen in figure 1.

Figure 1 Timber frame section
Figure 1 Timber frame section

Ventilating the cavity of timber-framed structures is achieved by using proprietary perpend ventilators (see figure 2) and are often left to the last minute or poorly installed. These ventilators are installed as part of wet-works i.e. brick laying or rendering. They are installed at the base (see figure 1) and at the top of the external walls at a minimum of 1.5m horizontal centres. These vents allow air to move inside the cavity and also the vents at the base will allow any moisture that is present in the cavity to be drained away.

Proprietary perpend ventilator
Figure 2 Proprietary perpend ventilator

Breather membranes are another essential element in ensuring adequate ventilation in a timber-framed cavity. As the name suggests it allows the structural timber of which the walls are made up of to breathe. As mentioned earlier, after a building is constructed there may still be some drying-out of timbers occurring within the walls, this breather membrane will allow moisture to pass through into the cavity and be drained away using proprietary perpend ventilators. The breather membrane also protects the timber-frame from moisture ingress during construction as it only lets moisture pass through in one direction (inside to outside). Regarding tears to the breather membranes, they must be repaired immediately especially if bad weather is expected. With both breather membranes and vapour barriers if they are damaged sufficiently then they should be replaced.To reduce the amount of moisture and avoid condensation within a timber-framed wall a vapour barrier or vapour check is installed (figure 1). This layer is fixed to the timber studs on the inside of the wall (warm side of the insulation) and joints should be lapped and taped sufficiently to provide a tight seal. While this layer will reduce the amount of moisture getting to the cavity, the drying-out of timbers within the wall will produce moisture which will be drained by the use of the proprietary ventilators as it will not be able to pass the vapour barrier to the inside of the property. If this vapour barrier is damaged, which can happen during transportation, installation, or when electrical/plumbing services are being fitted then it must be repaired to regain the tight seal. Holes for services in walls which are necessary can be taped and sealed, but care must be taken to ensure that this is carried out correctly as these are areas that moisture commonly can get through the vapour barrier and cause problems. As with services, all openings in walls such as windows must be treated in the same manner and sealed correctly.

Ventilation in floors

Ventilation in floors, especially suspended timber floors is very important so as not to facilitate the build up of moisture within the floor structure. This moisture build up can cause deterioration not only the timber joists but also any coverings placed over the joists. Ventilation in suspended timber floors can be achieved by installing vents… Continue Reading

I upgraded an old period house which had a dry tiled basement floor and some dampness in the walls and after renovation I now have dampness in the floor and mold forming on the carpet.

Answer. Most older houses had no or an inadequate damp proofing under the masonry floors and walls in the basement. When low levels of rising damp rises up through the basement floors the moisture would evaporate faster then the rate of the rising damp and the surface of the floor would remain dry, However, in… Continue Reading

I’m building an extension to the back of my mid terraced house and there is no storm water drain located in my garden, can I direct the rain water into the foul drain?

Answer. No, building regulations require that rain water and foul water are kept separate and that only foul water can go into foul water drains and likewise for rain water drains. The problem that you have is common in that about 50% of mid terrace houses, in that there is no rain water drain located… Continue Reading

Do I need planning permission to convert my garage to a kitchen, playroom or bedroom?

Answer. In most cases planning permission is not required and most garage conversions qualify as an exempt development defined under Section 4(1)(h) under the Planning & Development Act 2000. However, the garage must firstly be attached to the dwelling house and already be planning complainant as a garage. The garage conversion cannot be used as… Continue Reading

Do I need planning permission for an attic conversion?

Answer. In most cases planning permission is not required and most attic conversions qualify as an exempt development defined under Section 4(1)(h) under the Planning & Development Act 2000. However, while most attic conversion can be converted to storage use without the need to first obtain planning permission, the majority of attic conversions will not meet… Continue Reading

What Sellers and Buyers should know when organizing a building survey

Answer. This post will assist buyers and sellers of properties identify defects and other potential issues that the building surveyor will be looking for when your property is surveyed. If certain defects can be identified and repaired before the house is placed on the market for sale, it should prevent renegotiation taking place at a… Continue Reading

Misunderstandings about party walls and boundary walls in Ireland

We get numerous calls to our office from both home owners and adjoining owners asking about their rights and responsibilities pertaining to their party walls and boundary walls. Quite often our callers have researched their questions and concerns over the internet or from friends and normally end up being more confused at the end of… Continue Reading

Where is your boundary line?

Where is your boundary line?

Answer The Land and Conveyancing Law Reform Act 2009 is designed to help neighbours resolve any disputes about works on or near the boundary line between two properties if they themselves cannot come to an agreement. Boundaries are denoted Ordnance Survey plans and also on the title plans on the title deeds. Each registered property… Continue Reading