The Dangers of getting it wrong

Bonded bead Vs Urea-formaldehyde Vs Mineral Wool

Mineral wool and expanded polystyrene systems are certified by the British Board of Agrément (BBA).  UF foam systems are covered by British Standards (BS 5617, BS 5618). The BBA also assesses and regularly monitors the performance of Approved Installers. Before you go ahead, we will  ensure that cavity wall insulation is only installed where it is appropriate and to ensure that the price is accurate, the designers of each cavity wall insulation system have a strict assessment procedure.

This procedure involves:

  • Determining whether the wall is in fact a masonry wall with unfilled cavities.
  • Inspecting the general condition of the external wall.
  • Identifying any constructional defects that first need to be remedied.
  • Checking on the inside of external walls to see if there are any existing dampness problems that need to be remedied.
  • Checking any penetrations of the external wall, e.g. for flues and air ventilators.
  • Finding out if the cavity of a directly adjacent house has already been filled, e.g. in a terraced or semi-detached house.
  • If necessary for the insulation system, checking the exposure of the wall.
  • The standard of wall construction and its condition will be taken into account in the assessment of suitability. Defects within the wall construction such as bridged cavities, as well as other defects, e.g. failed pointing or broken guttering that causes the top of the wall to be saturated, will be picked up during the assessment and should be rectified before filling begins.

cavity removal

Cavity wall insulation can be the most cost-effective method of reducing fuel bills – but installed incorrectly it can cause expensive problems.
It can lead to damp developing and the cost of rectifying this can outweigh the savings made.
House-builders began regularly constructing properties with cavity walls from around 1920, and two decades later it became standard industry practice.


But poor wall cavity insulation can cause an array of problems. Damp can lead to crumbling plaster and fungal decay, and later to more serious structural and timber erosion.
Increasingly rain-lashed winters have resulted in an increase in reports of damp issues in properties. A likely cause of damp is the bridging of the cavity by the earlier installed insulation material. Moisture penetrates into the cavities – more noticeably on weather prevailing walls – and damp gradually builds over the years as the insulation material becomes saturated.

We take a proactive role to prevent damp occurring. By using machinery which blasts compressed air into the cavity walls, the problematic debris and old insulation is removed. It is usually possible to drill through old holes in the brickwork where the original insulation was inserted.
The debris blown out of the cavity and collected in bags fixed to the external wall. The whole process can be completed within one or  two days – depending on the size of property – and with minimum disruption and mess.

Urea-formaldehyde foam insulation

Urea-formaldehyde foam insulation (UFFI) can make a great synthetic insulation. It is basically foam like shaving cream and easily injected into walls with a hose. It is made by using a pump set and hose with a mixing gun to mix the foaming agent and resin. The liquid foam is sprayed into areas in need of insulation. It hardens within minutes but cures within a week. UFFI is generally spotted in homes built before the seventies; one should look in basements, crawl spaces, attics, and unfinished attics. Visually it looks like oozing liquid that has been hardened. Over time, it tends to vary in shades of butterscotch but new UFFI is a light yellow color. UFFI shrinks significantly and dries with a dull matte color with no shine. It will be a dry and crumbly texture.

Safety concerns

Urea-formaldehyde foam insulation (UFFI) started being used in the 1970s. Homeowners used UFFI as a wall cavity filler at the time in order to conserve energy. In the 1980s, concerns began to develop about the toxic formaldehyde vapor emitted in the curing process, as well as from the breakdown of old foam. Emission rates of more than 0.1 parts per million (ppm) takes a toxic toll on humans. Consequently, its use was discontinued. The urea-formaldehyde emissions decline over time and significant levels should no longer be present in the homes today. Modern replacement options include melamine formaldehyde resin and polyurethane.

UFFI was usually mixed at the location of use while constructing the home’s walls. It was than injected inside the walls, the curing process occurs, and the final product acts as an insulating agent. Historically, less information was known about the toxic health effects of formaldehyde, sometimes extra formaldehyde was added to the mixture to guarantee that the curing process would occur completely. UFFI is not a well sealed product; it is put into place and left there in the open. It is dangerous when becomes wet or exposed because this is when levels of formaldehyde can be released into the home. UFFI has an unfortunate direct link to temperature, they are positively correlated. When temperature rises, the levels of formaldehyde that leaks will also increase. Solutions for positive tests (testing for formaldehyde emissions in the air) of UFFI leakage is to seal off the outlet for the vapors. One would seal all the cracks and apply multiple layers of vapor barrier paint, and then further covering this with mylar of vinyl paper. Aluminum foil is a useful alternative for barricading vapors. Removal is a costly and tedious option for UFFI and would require a replacement insulation installation.

The Health & Safety Executive advises against Urea Formaldehyde Foam Insulation

Mineral Wool

Mineral wool is the "cheaper option" used by most installers.  The main drawback is that the fibre can settle in the cavity over time, leaving "cold spots". Research has shown that up to 40 per cent of houses insulated with blown mineral fibre can be affected. Some readers have argued that a few cold spots are a small price to pay for better insulation overall. The danger, however, is condensation. Because the rest of the house is better insulated, the internal temperature can rise and, with it, relative humidity. This means wall areas that are slightly cooler than the rest can be subject to condensation and black mould, which can give the impression of penetrating dampness. Areas commonly affected are those below and between windows, and at ceiling level in upstairs bedrooms.

Blown mineral-wool fibre has to become only slightly damp (around one per cent by volume) to lose all of its insulation properties. Any damper than this, and it will actually start to draw more heat out of the house than if the insulation were absent.

Bonded Beads

The most effective energy saving solution. With this system thousands of small polystyrene beads are blown into the cavity space and bonded using a binding agent or PVA adhesive. The binding agent holds the beads in place and stops them settling or coming out of the cavity if any structural work is carried out at a later date.

EPS beads have very good thermal properties and are water repellent, they do not rot or decay, and do not provide nutrient value for insects, parasites, or animal and plant life.

The latest EPS Polystyrene bead systems provide an alternative to mineral fibre. The system is fully guaranteed and is covered by a CIGA guarantee


  • Provides a high level of thermal efficiency – warm in winter; cool in summer
  • Reduces energy consumption and therefore heating bills
  • Less demand on boilers
  • Reduces condensation and black mould growth
  • No maintenance required
  • No disruption to inside of your home


Cavity wall insulation is the most cost-effective low risk energy efficiency measure for existing housing, after loft insulation. Any cavity wall, if poorly constructed, is likely to suffer from damp problems. There is no evidence that filling with cavity wall
insulation increases the risk of rain penetration. Good maintenance of the house and the correction of building defects are the keys to success.

Most cavity wall insulation systems are suitable for use in all parts of the UK without restriction. For those where exposure is an issue, assessment methods are
available to ensure that the installation will perform satisfactorily.

The cavity fill installation causes little disturbance and can usually be carried out in less than half a day. It is carried out by Approved Installers whose work is
backed by a dependable 25 year guarantee from the CIGA. Customer satisfaction is high – more than 95 per cent of homeowners who have cavity wall insulation
would install it in a new house if they moved.

Bonded bead far outweighs the properties of mineral wool in thermal rating and is not subject to "slumping". Urea-formaldehyde foam insulation is now frowned upon by most sectors in the industry due to its potential hazzardous properties and less effective thermal qualities.

New building regulation requirements (Nov 2006) specify that all New Build Properties are required to have a 'U' Value of 0.27. ( The 'U' value is the rate at which heat passes through a wall, the lower the 'U' value, the more heat that is retained.

Typical U Values Mineral Wool (lower Number = better)

Existing uninsulated walls

Uninsulated value

50 mm cavity insulation 65 mm cavity insulation
Brick cavity wall



Brick and lightweight block



It can be seen from the above that it is most effective where the initial U value is high. The treatment will clearly be cost effective in the first situation; the second one is less certain.

Typical U Values Bonded Bead  lower Number = better

External Wall Construction
Cavity Width 75mm
Cavity Width 80mm
Cavity Width 90mm
Cavity Width 100mm
12.5mm Plasterboard on Dabs, 100mm AAC Block (I = 0.15) & Brick Outer
12.5mm Plasterboard on Dabs, 100mm AAC Block (I = 0.19) & Brick Outer
12.5mm Plasterboard on Dabs, 100mm Medium Density Aggregate Block ( I= 0.47) & Brick Outer
12.5mm Plasterboard on Dabs, 100mm Dense Concrete Block (I = 1.13) & Brick Outer
12.5mm Plasterboard on Dabs, 100mm Lightweight Block (I = 0.09) & Brick Outer

Bonded bead cavity wall insulation has an affective thermal conductivity of 0.033Wm-1K-1 and will satisfy the new building regulations. i.e. 100mm cavity = 0.27u Value. The heat retained within a building as a result of the Silver cavity wall insulation, will result in 40% more fuel savings. Bonded bead cavity wall insulation gives 15% - 20% better Thermal Insulation compared with other insulation techniques.

Diamond Bonded bead can achieve up to 73% more efficiency


Bonded bead far exceeds any other form of cavity insulation. Diamond Bonded Bead has the distinction of being the best material to use for thermal properties


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