Reducing your bills with cavity wall insulation

Cavity wall Insulation blown into a wall

Cavity wall insulation using EPS bonded beads

Insulating the cavity in your external walls can be one of the most cost effective ways of reducing your fuel bills. Up to 30%-35% of your heat can be lost through the walls of your home - and with a range of grant funding available there has never been a better time to cut your bills.

Here's how we can help you:

  • Provide advice on the various insulation systems available
  • Recommend one of our approved contractors
  • Explain how the ECO, Green Deal and grant schemes work
  • When you ask us for advice about cavity wall insulation or loft insulation, a qualified surveyor will survey your home and advise you on the suitability of cavity wall insulation and which system is appropriate for your home.


There are three main cavity wall insulation systems available in the UK: today, but which is the most suitable for your home?

Mineral wool blown fibre insulation

Mineral fibre Insulation

Mineral fibre Insulation

Mineral wool Insulation, also known as Rockwool, White Wool or Glass Wool is made from spun volcanic rock or glass. It's an entirely dry system which uses granulated fibre blown into an external cavity wall to a predetermined density. The mineral fibre is treated with a water repellent during the manufacturing process.

The material is blown into the cavity space through a series of holes. As with all forms of cavity wall insulation the work is carried out externally. Before installation can take place the cavity must be inspected to ensure the walls are suitable.

This system has been used widely throughout the UK since the 1960s. With a proven track record of performance, mineral fibre is the most cost effective system and accounts for the majority of work carried out in the UK - and it's guaranteed by the Cavity Guarantee Insulation Agency (CIGA).

Expanded polystyrene (EPS) beads

bonded bead cavity wall insulation

Bonded bead cavity wall insulation

Regarded as a high quality and premium insulation 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.

During installation the free flowing beads flow very easily into the cavity and so can often be used in 'problem' properties when the cavity might not be suitable for standard mineral wool.

Bonded beads are often used to insulate properties made from stone or where the cavity is narrower than normal than the 50mm minimum allowed for mineral wool. Bonded beads are a more thermally efficient form of insulation than mineral wool.

EPS beads have very good thermal properties and are water repellent. Injecting bonded EPS beads requires fewer drill holes than either the wool or PU foam systems.

The latest EPS Polystyrene bead systems provide an alternative to mineral fibre. The system is fully guaranteed and is covered by either a CIGA guarantee or the manufacturers own warranty.

Polyurethane (PU) injected foam

PU foam Insulation

PU foam Insulation

Not to be confused with the old UF or Urea Formaldehyde foam system popular in the 1970s, Polyurethane foam is a form of wall insulation suitable for 'random stone' walls or other properties with non-standard cavities. It has excellent thermal properties and with a 'closed cell' structure it is totally water repellent.

This system has been used extensively through-out the UK for over 20 years and has the added advantages of enhancing the structural strength of walls. Because it binds to the inner and outer walls it can be used in walls where the wall ties have failed. The material is injected into the cavity and expands filling all voids and gaps. It requires the most dense drill pattern of the three systems discussed here - and is also the

Read more about the survey process >

It's essential that an experienced surveyor assesses the suitability of the property for cavity wall insulation. Not all houses are suitable for insulation because of age, existence of structural defects or exposure to prevailing weather.

Failure to provide adequate ventilation in your loft can cause condensation and excessive dampness ultimately leading to problems such as wet or dry rot and infestation of wood boring insects. Our surveyors are trained and qualified to assess the suitability of a property for installing additional home insulation.

The survey process

The following points will be checked during our cavity wall insulation survey:

  • The type of wall construction and the width of the cavity
  • The total wall area
  • Type of structure, eg: brick and breeze; concrete block; or stone outer wall
  • Services through the cavity, eg, gas flues or cables
  • The cavity is free of debris
  • The damp course is not defective
  • The cavity tops are sealed
  • Condition of the wall structure to identify potential defects
  • That ventilation is adequate underneath ground floor timbers
  • That ventilation is adequate for gas appliances (that meet certain criteria)
  • That no damp is present: we test all properties as a matter of course
  • Stone built houses require very careful examination

The following points are checked during a survey for loft insulation:

  • Existing depth of any current insulation and the extra thickness required
  • Area of insulation required, and any boarded areas
  • Length of live pipe work to be insulated
  • Number of cold water tanks to be insulated
  • Position of the hatch relative to tanks and pipes
  • Whether the loft has adequate ventilation
  • Roof leaks or damp present
  • Assessment of existing electrical wiring and spotlights in bathrooms nee

By working with a range of reputable contractors, and using several systems, we can recommend the one that's right for your house. Based on your home's size, style, age and location we'll advise you on the most suitable product for your home.

When we arrange a free quote for cavity wall or loft insulation, a qualified Thias energy surveyor will advise you on the best course of action. Read more about the survey process >

The current standard for loft insulation is for it to be at least 270mm deep (around 1'). Very few houses we see meet this standard, but a correctly insulated loft can reduce your heating costs by up to 25%.

Insulation for stone houses

We provide EPCs and advice on the ECO scheme, (Energy Company Obligation), and advice on hard to treat properties covered under the ECO scheme.

bonded bead cavity wall insulation

Bonded bead cavity wall insulation

For houses built with random stone walls we recommend a detailed assessment before any insulation is considered. You can either use bonded polystyrene beads or polyurethane foam as they offer very good thermal properties and are suitable for random or coursed stone walls.

Polyurethane foam has the added advantage of increasing the structural stability of a wall, whereas bonded beads is the more cost-effective option.

For properties with stone walls a more detailed examination is required.

Specifically we check, that for each wall:

  • The cavity is of sufficient width to ensure it is fully filled with insulation, since by their nature stone walls may have an uneven cavity
  • There are no obstructions in the cavity
  • There is adequate sub-floor ventilation
  • There is no evidence of ‘bridging’ of the cavity, which would allow dampness to permeate from the outside to the inner wall

In our experience random or coursed stone walls tend to be either:

  • Suitable for cavity wall insulation
  • Requiring some localised repair (eg, resolving a dampness issue) before cavity insulation can be installed
  • Not suitable for insulation (eg, because of inconsistent cavity width or obstructions)

As part of our survey we will look inside the cavity with a check scope or boroscope and advise you on the options available.

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