Improving Levels of Loft Insulation

CONDENSATION IN ROOF SPACES IS GETTING MUCH WORSE WITH INCREASED LEVELS OF INSULATION.

It is important to remember that the majority of moisture we produce in our homes is created in a gas form as water vapour. Unlike water in a liquid state, water in a gas state can spread easily causing condensation, which may result in damp and decay to vulnerable building materials and possessions, especially the case in our roof spaces.

As the laws of gasses state, warm air occupies a larger volume than cold air and therefore is capable of holding more water vapour. Warm air is also less dense than cold air, so it will rise carrying with it the water vapour we have produced.

This warm moisture laden air typically created in our kitchens and bathrooms rises through the building and into the roof space, usually through un-insulated loft hatches, gaps in and around ceiling lighting and pipe work and diffusing through plasterboard ceilings.

When this warm air meets the roof environment it cools, and as explained, the cool air is unable to hold the same amount of vapour as the warm air once did, so the air the expels excess water as liquid condensate – a process known as condensation.

Condensation in a roof will form on the coldest parts of the roof structure such as; the underside of felt membranes, timber structures and gable elevation walls. It is estimated that upto 30% of the moisture we produce in our homes finds its way into our roof spaces.

With recent government grants for improving insulation, most houses will now have some form of loft insulation being either, rolled fibreglass, polystyrene, or spray foam and in recent years recommended standards have increased to 250 mm (12 inches).

Obviously however, insulating our attic ceilings results in our roof spaces becoming cooler as heat transfer from our living environment is reduced, which can increase the likelihood of condensation. It also common for insulation to extend into the eves of the roof to prevent cold air intrusion cooling of the ceilings edge, well known condensation and mould prone areas.

Insulating the eves can block off natural ventilation which would have occurred, through soffit vents or vented facia strips. Common bitumen felt membranes used many years ago as secondary protection to the roof coverings are also vapour barriers, which prevent moisture within the roof diffusing out, resulting in trapped moist air condensing on the underside of the felt, where water drips upon ceiling insulation and rests against roof timbers causing decay.

So, what is the answer?

Not to insulate our roofs and ceilings and let warm air keep the roof toasty? Prevent covering the eves strip allowing ventilation, yet cool our ceilings leaving them susceptible to condensation and mould?

Obviously not, It is however, important to remember that whilst we try to become more energy efficient by improving our insulation levels that we do not obstruct the ventilation in place. When considering improving our insulation levels we must ensure that the existing ventilation is adequate and not compromised or improved where necessary.

If you are improving your loft insulation this winter check the following;

• Eliminate cold spots on ceilings by ensuring the loft insulation is evenly laid
• Where insulation extends into the eves ensure ventilation into the roof is not compromised.
• If eves vents are obscured use alternative means of venting the roof such as; gable vents, ridge vents or vents within the roof covering.
• If installing vents within the roof covering ensure the area of low level vents is roughly twice the area of high level vents and never fit ridge vents or high level vents as the only means of ventilation.
• Modern breathable felt membranes such as Tyvec are available and used in all new build properties. These clever membranes allow vapour to permeate out of the roof whilst retaining a water tight outer layer to prevent water from a defective roof covering coming in. If you are considering replacing your existing roof covering or simply re-roofing ensure your builder uses a breathable membrane to reduce the risk of condensation.
• Ensure where possible potential paths for moisture vapour to enter into the roof space are sealed
• Insulated your loft hatch

If you suspect you have a damp problem and need professional advice or repair, don’t gamble call the experts; Dryfix Preservation Ltd “Yorkshires Leading Damp & Timber Specialists” on 01904 791388 or visit our website www.dryfix.net

Russell Rafton C.S.R.T / A.Inst.SSE
Dryfix Preservation Ltd – Surveyor