Cavity Wall Insulation and Home Energy Saving

Sustainable Energy Ireland (SEI) currently operates two home energy conservation programs where the participant house owners may be reimbursed the total cost they incur while carrying out certain home energy improvements. One such improvement is the cavity wall insulation. Cavity walls provide a convenient structural design to support wall insulation material.

Cavity Walls
Cavity walls are external building walls which incorporate an air gap which may be within the wall structure itself (for e.g. Hollow block walls) or between two solid walls (or between two partitions having a narrow air gap separating them).The latter technique was widely used in houses constructed between 1932 to 1982.
Almost all houses constructed after 1982 adopted the cavity wall technique with or without the use of insulation.

Why do you need insulation in cavity wall?
The wall cavity maintains an air gap which is a good insulation. (In fact it is about the best available conveniently and almost all other manufactured insulation material incorporates air bubbles or spaces in order to gain this advantage).When the cavity width between the two walls exceed a certain critical dimension the air within the gap start moving about due to convection (convection currents) which start assisting heat transfer from the warmer to the colder side rather than blocking it.

Porous insulation fill will restrict the air movement within the cavity providing optimized insulation quality.

How to find out whether your house has cavity walls
All houses built during the last 25 years are almost certain to have cavity walls. It is possible these may be insulated too. Houses built during the 50 years prior to that are also likely to have cavity walls but may not have any insulation.

A sure giveaway sign is the brick pattern of the exterior wall. In general wall bricks are laid in 3 patterns. viz;

• Stretcher bond


• Flemish bond

And,

• English bond

Of these only the stretcher bond patterned brick walls will have a wall cavity. A stretcher bond patterned brick wall will have the bricks laid flat on side and in a linear manner i.e. bricks laid end to end.
Another tell tale sign is the width of the total wall. Due to the incorporated cavity the width is in excess of the normal 300 mm width you would expect it to have.

It is always better to get a skilled person with proper tools to give advice on these matters. Normally they drill holes in the wall and collect data to find out the details of the air gap, insulation material (if any), and the present condition of it.

Types of insulation for cavity walls
The commonly used materials are;

• Fibreglass or mineral wool with short strands


• Cellulose loose fill or stabilized cellulose

• Phenolic and other Synthetic foam cavity board –(Used in new constructions only).

Cavity wall insulation if it is a retrofit in an existing house will not take more than 3 or 4 hours. Of course it has to be handled by a skilled person with specialized tools. They would drill holes in the existing external wall at regular intervals, insert a special nozzle and blow short strands of insulation material in to the wall cavity. If the house is being constructed anew phenolic foam rigid board or expanded polystyrene foam boards too may be used.

John Mahoney is a freelance author who writes about various RENEWABLE ENERGY topics including Cavity Wall Insulation .For more info contact www.techstore.ie