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Building Your Home With Timber FAQ

Building Your Home With Timber FAQ

Is planning permission needed for a timber building?

Whether a building requires planning permission or not depends on the location, size and use to which it is to be put.  To build a separate building on land for use as a home requires planning permission.  Building a garden shed may not require planning permission but is not suitable or permissible under planning law to use as a home.  It is best to check, ask an expert or the local council.  New homes do require planning permission.

Are timber buildings economical?

The costs of constructing homes are similar for all types of construction.  No significant savings can be expected for building using timber.  The principal difference between building types are typically confined to external walls.  External walls can constitute less than thirty percent of total building costs, the remaining seventy percent includes foundations, drainage, roof, windows, doors, electrical installation, plumbing, fitted furniture, groundworks and decoration.  A garden shed compared to a home may appear economical, but costs offered should be examined carefully.  Timber used in construction in Ireland is typically imported.  The most economical buildings use materials most suited to the local environment and locally available.  Timber in some cases may be more economical.

Do I need an architect?

Building Control Amendment Regulations of 2014 (Ireland) require of those building homes to assign a certifier and a builder who are competent and qualified to provide their services.  There are no qualifications recognised or controlled in Ireland for builders or tradespeople (2019) other than relating to heating and electricity.  Assigned Certifiers and Designers must have recognised qualifications.  Engineers, Architects and Building Surveyors are the only professions permitted to take the responsibility of assigned designer or certifier.  These all require years of education and training and the practitioner must be registered.  In building anything that is subject to building regulations it is vital that a suitably qualified professional be appointed.  Architects, Engineers and Building Surveyors offer different skills.  To optimise the design potential the most qualified is an architect.  Structural design and underground drainage require the services of an engineer.  Building Surveyors should be familiar with regulations and the building science, as should any professional offering the services of Assigned Certifier or Designer.  It is the building owner’s responsibility under law to appoint someone they know to be competent.  In this regard it is important that the principal professional or project leader be as familiar with all requirements as possible.  Unless you are an expert, you do need an expert.

Of the many systems for timber building, how do we choose?

The simple answer to this is that you don’t.  Unless of course you have the qualifications to choose.  Marketing material examined offer, single solid log walls, glulam walls, twin wall systems with insulation filled cavities, timber frame with solid log external skin, cladding, metal roofs, timber floors, double glazed windows and so on.  There is a large choice and cost alone should not be a deciding factor.  Technically, many of these are no more than garden sheds.  These are typically unsuitable as homes, offer little insulation or moisture control and often have costs that relate only to the bare building only.  Foundations, electrical installation and plumbing is often not included.  The prices quoted are for simple garden sheds.  Some of these are offered with insulation.  Of the systems inspected, the levels of insulation are often very low and neglect the effects of moisture movement through building structures.  A simple garden shed often has similar internal temperatures internally to that externally.  In such a situation there is little thermal movement that could result in damp.  The capacity of air to hold water increases with higher temperature.  More worrying, this capacity reduces with lower temperature.  As air moves from warm to cold spaces, or from inside a home to outside, it reaches a condensation point at which the air temperature can no longer sustain the levels of moisture.  This can occur within the building fabric and often does.  Quality timber technology (or any quality building technology) controls this movement of moisture.  Much of the insulated timber technology inspected on site for low cost buildings does not address this tendency.  Interestingly, those simple garden sheds that have been insulated often increase the risk of this moisture movement impacting negatively on the structure.  Where this occurs within the structure, it is called interstitial condensation.  The build up of moisture in hidden parts of construction can be calculated and needs to be controlled.  This can be controlled by ventilation, after carrying out calculations where condensation is most likely to occur.  This will inform as to where ventilation should be.  Where this ventilation is not provided, moisture will build up.  This can result in black mould on wall surfaces, or moisture in the hidden parts of walls.  This in timber construction can be detrimental and in cases dangerous.  The Berkeley balcony collapse in California on investigation was deemed the result of inadequate structural ventilation resulting in dry rot (Serpula Lacrymans).   Dry rot completely destroys timber and thrives in the absence of ventilation.  Much of the structural detailing examined in cheap timber construction supports the development of dry rot.  The least effect of this is seriously reduced life span for buildings so constructed.  As with Berkeley, the most serious result can be fatal.

Understanding of the science of building is vitally important as buildings become more complex.  The complexity arises due to the need to conserve energy.  Passive methods are those where no active measures are taken, such as the physical build up of external walls, floors or roofs.  The science relating to the movement of moisture must be understood.  The science relating to active solutions such as ventilation systems must also be understood for as building fabric becomes more efficient, room or space ventilation becomes more important.  These factors render simple technologies for the most part obsolete.  The best choice you can make is to choose an independent expert.

Are timber buildings environmentally sustainable and energy efficient?

The levels of insulation under current building regulation with reference to TGD Part L (Technical Guidance Document Table 1, the maximum elemental U-Value for external walls is 0.21 W/m2k (watts per metres squared kelvin).  To achieve this with simple log buildings, the factors that must be considered includes the durability of the timber used and the thickness of the wall.  Sustainability requires durability.  For instance, cedar is a highly durable timber which offers excellent insulation properties.  In order that a solid timber building complies with regulations the thickness of a cedar wall would need to be in the order of 420mm.  For comparison with more widely available timber species, a solid less durable spruce wall would need to be about 600mm thick in order to comply.  Cedar is considerably more expensive.  Also, thicknesses as would be required are not generally available commercially and would need to be ordered specially from very specialised suppliers.  Factory assembled elements that offer similar performance can be available but again generally only on special order.  To reduce this thickness would require the addition of insulation, which when carefully designed and applied could result in a wall thickness in the order of about 250mm.  Less than this is possible, however the costs and technical complexity increase dramatically with any thickness below 250mm.  Any wall therefore less than 250mm is likely to fail either in terms of moisture damage or insulation rating.  Walls of 250mm if poorly designed may result in failure.  Timber is a sustainable building material and if correctly detailed and constructed can last generations.  Energy efficiency requires high levels of insulation and air tightness.  Sustainability when applied to any building material is directly proportional to the resultant life span of the building.  It is therefore possible to have an environmentally unfriendly concrete building being more sustainable than some timber buildings.  Timber buildings if designed and built correctly can be highly sustainable and energy efficient.

Are timber buildings simple to construct?

Some marketing implies that timber or log building is a cost effective and technically simple way to build a home.  As noted above, timber construction can be simple technically though with generally unavailable 420mm thick cedar logs would be extremely expensive.  Cutting logs to fit snuggly takes experience and skill, as does placing them.  This can be technically simple but difficult to execute.  One spruce log section of the size noted above 300mm long could weigh more than two hundred kilograms.  Buildings complying with current building regulations are not simple to construct.

Reliable information required to sustainably and economically construct buildings is not easily available.  Misinformation abounds!  Technical and scientific expertise is required to evaluate the plethora of offers available.  Many marketed building systems fail it appears as a result of an absence of the expertise required.  Some do offer sustainable solutions, those who do are happy to be exposed to professional and expert evaluation.  The construction of garden sheds as homes being tabled as a viable option is an insult and injury to society and the absence of proper control worrying.  It falls legally on the building owner to ensure compliance and the building control regulations require local councils to examine fourteen percent of buildings being constructed.  This offers a security to those being inspected by the councils.  It relates to fourteen percent of buildings that are notified to the council and has no bearing on those being built outside the rules.  The recourse to the councils in dealing with buildings illegally constructed is to enforce their removal.

In brief, let the independent professionals do what they do, and enjoy the benefits.

Author – David Moran Architects