Category Archives: Blog

Ancillary Product – Cavity Wall Brushes

What are cavity wall brushes?

Cavity brushes are installed on all party walls between joining properties that have not been previously insulated. They consist of two wires twisted together at the centre with filaments or bristles radiating from the core.

Cavity brushes are normally installed at the front and back of the property, before installation takes place. Blown insulation should not commence without them. The product was designed to separate properties, providing a substrate within the cavity wall for the insulation to be installed against. It prevents any insulation materials collapsing into the neighbouring property while retrofitting insulation.

Can cavity wall insulation be extracted from a property without interfering with the joining property?

It would be very unlikely but not impossible.

For more technical information regarding joining properties or to book a site survey, please leave your contact details below.

Removing urea-formaldehyde foam cavity wall insulation

The use of urea-formaldehyde foam insulation was a popular choice in the late seventies and early eighties to help improve the energy efficiency of properties. This type of insulation could be injected into older cavity walls, where no existing cavity wall insulation was present – vastly improving the thermal performance of the wall.

Urea-formaldehyde was one of the first materials used to retrofit cavity walls with insulation. It was popular because it was easily injected (it goes in almost like shaving foam before setting solid) and so there was no impact on the appearance of the property.

An estimated 1.5 million properties were retro-fitted using urea-formaldehyde cavity wall insulation. Unfortunately it is becoming more and more common for this type of cavity wall insulation to fail. We are going to discuss the reason for this below.

Problems associated with urea-formaldehyde cavity wall insulation

When urea-formaldehyde was injected into old properties, it was as a mixture of foaming agent, resin and compressed air. The foam tended to solidify in just a few hours and then cure over the following week or so. The problem is that this type foam shrinks as it cures – and shrinks significantly. Often this issue only came to light when the homeowner revealed the cavity (by replacing windows etc.) but it meant that there were areas across the wall surface where there was no longer any insulation, resulting in cold bridging.

The other issue with urea-formaldehyde is that it also breaks down as it gets older, changing from a solid foam mass to a crumbly powder. This normally means the insulation slips down with the cavity leading to the same sort of issues associated with shrinking – cold spots across the wall area where there is no insulation.

The final issue with the urea-formaldehyde cavity wall insulation was the release of formaldehyde as it broke down – formaldehyde is proven to lead to a variety of adverse health effects impacting the eyes, nose, and respiratory system.

Extraction4Homes – getting to the root of the issue!

At Extraction4Homes, as you might expect we have a huge number of customers getting in touch with us regarding urea-formaldehyde. For us it was very important to find a method of helping this type of customer  – in terms of advice as well as introducing a safe procedure for removal or extraction of urea-formaldehyde from the walls.

It became apparent on our site surveys and specific investigations into this type of insulation that the breakdown of urea-formaldehyde was far more apparent in south-facing walls.  Our investigations suggest that this is a result of greater exposure to direct sunlight on these brick faces, increasing the working temperature of the urea-formaldehyde. This seems to have contributed to a much faster breakdown of the material over the years, reducing the urea-formaldehyde to a powdery dust. This theory was backed up by evidence from our surveys that commonly found almost perfect insulation within north facing walls (or in much better shape than the equivalent south facing wall of the same property).

So if customers come to us now regarding this type of cavity wall insulation, our first task is to confirm that this type of insulation really is in place.

Identification urea-formaldehyde within property

To an experienced surveyor, urea-formaldehyde injection holes can be seen within the mortar joints of the building – but over years of exposure to the elements, these injection holes can be very hard to identify.  The most common place to identify the urea-formaldehyde is within your loft area, which tends to be the most common location for overspill around the eaves of the roof due to the open cavity extending into this space.

By drilling a series of pilot holes around the building, we can also us a borescope camera to identify the urea-formaldehyde and confirm its current state.

If it is confirmed the urea-formaldehyde is within the cavities, we can then remove this if the customer so desires.

Safe removal urea-formaldehyde

Extracting or removing urea-formaldehyde from a property is no easy task, with many extractions companies refusing to undertake this type of work for many reasons including:

  • Timescales – removing this type of insulation takes time
  • Internal preparations – we need to be sure that the dust produced from the extraction work doesn’t enter the inside of the property
  • Sheer hard work – removing this type of insulation is far more difficult than other cavity wall insulation.

For us, preparation is absolutely key – we also inform the home owner of possible disruption, which may include moving out whilst the work is underway.

Our preparation includes the following activities:

Loft area – all eaves are sealed and missing brickwork is sealed within gable ends. We also cover all personal property with dust sheets – the aim is to contain the urea-formaldehyde as much as possible.

Windows & Doors – All windows and doors are taped and sealed with clear polythene plastic with the aim of containing the urea-formaldehyde and reducing exposure of formaldehyde to the the internal environment

Room Ventilation – Similar to windows and doors, all room ventilation is taped and sealed with clear polythene plastic – all gas and solid burning appliances should not be used while ventilation is blocked. We then perform a spillage test pre and post extraction to ensure the ventilation is still working as it should.

Other Services   – Overflow pipes, waster pipes, washing machine outlets and tumble dryer outlet are all covered to contain the urea formaldehyde.

Unfortunately it is almost impossible to contain the urea-formaldehyde 100% while the extraction process takes place, because the extraction process involves breaking down all the existing insulation into a fine white dust which is then vacuumed out of the cavity. However we try to minimise this best we can using the methods mentioned above.

Interested in using our services?

For more information regarding our survey packages and technical support for removal of urea-formaldehyde, please call us on o208 819 9152 or fill in the form below and one of our team will be in touch shortly.

Thermal Survey

Thermal Imaging Technology

Using Thermal Imaging Technology, Extract4Homes can identify voids within cavity walls after retrofit installation of insulation. This may provide evidence in cases of  incorrect installation or breakdown of older types of material (such as formaldehyde foam). Many companies are very quick in offering their services to extract defective materials at a high cost

So we need to look at all possible options regarding CWI problems before looking into extraction process

Cold Spots

Many householders suffer from cold spots appearing on the internal leaf of their property, after blown insulation has been injected. Using a thermal imaging camera, we are able to detect voids within the insulation without removing external bricks. As this is a non-intrusive survey, it does not affect any guarantees held with the property.

Taken with SM-N9005, Android 5.0

The thermal picture above shows a cold area within the wall we surveyed using the thermal camera on the internal leaf  – and a void within the insulation. Leaving a black residue to the inner wall in a form of a circle – we refer this to cold bridging within the trade.

This could be caused for many reasons:

1. The injection point has not been filled with insulation.

2. There is bridging of the cavity (rubble within the wall) that prevents the insulation filling the area.

3. The drilling pattern is incorrect – the system design set by the manufacturer of the product installed has not been followed. An example drilling pattern is shown below:


4. The insulation material is the wrong size for the cavity width.

5. Building alterations have been made after installation (for instance new windows or door), causing the insulation to collapse.


Further investigation using a borescope camera was conducted via the company which originally installed the insulation. A void within the insulation was found to be causing the problem.  The affected wall area was then re-blown, filling the unfilled cavity. The customer had three quotations for the removal of the insulation – all over the 2.5k which was not required with this case.

A thermal survey identified a small void within the insulation, which was easily rectified, saving the customer thousands of pounds.

So which steps should you follow to resolve a CWI problem ?

Contact the insulation company with your concerns – this should be followed up with a site visit.

If you are unsuccessful with the insulation company or the company no longer trades, contact the guarantee agency.

A thermal survey can save thousands of pounds by saving you the cost of extraction. Cold bridging can rectified at very little cost, leaving you with a energy efficient property to enjoy.

For more information regarding thermal survey package and technical support, contact us via the enquiry form below.


Why is ventilation necessary?

All Buildings are built with ventilation in mind, with different types of vents which serve slightly different purposes, however broadly the vents are there to help achieve a few common goals. First the increased air flow provided by the vents should help prevent condensation build up in the home (which can lead to mould). Secondly, older open flue boilers and gas fires rely on good ventilation in the room to create the right environment for the fuel to burn – a lack of oxygen can cause the fuel to burn in a different way which produces harmful by-products. Homes with suspended timber floors will have ground level vents that allow the air to circulate around the floorboards to prevent the floor boards rotting. Finally good ventilation actually improves the quality of the air for the occupants – rooms avoid becoming too stuffy.

When cavity walls are retrofitted with cavity wall insulation, it is quite common for these vents to be inadvertently blocked – but depending on the type of vent this can result in dangerous consequences – so here we are going to look at the different types of vent and let you know which ones should be kept and which ones can be safely closed off.

Floor vents are critical to prevent rotting!

Firstly it is vital that the air vents which are installed to ventilate the area below the floor are not blocked. If these vents have become blocked by debris in the cavity, insulation or have been deliberately sealed using silicone sealant or similar then the air flow beneath a timber floor will be restricted or completely removed which can lead to floor timbers rotting over time.

Always keep vents involved in combustion open!

Above floor level the vents do have different purposes, but the most important type of vent is the one involved in helping achieve necessary airflow for combustion – these cannot be blocked ever!

Normally these types of vent are sleeved – meaning that the vent is continuous from the inner skin of bricks to the outer skin – however this isn’t always the case. If the cavity is filled with insulation retrospectively and this type of vent isn’t sleeved then the vent can become blocked with the new insulation – and unfortunately this type of oversight is becoming more and more common from sloppy cavity wall insulation installers. This type of vent should never be sealed from the inside or the outside; the installer needs to perform a spillage test pre and post installation to ensure the vent is still working as intended once the cavity wall insulation gets installed within the cavity.

Likewise, vents that are used to help ventilate rooms with gas or wood burning appliances should always be sleeved if the appliance in question is situated within the room and has a rating of 5kw or more – this  includes open fires. It is the responsibility for the cavity wall installer to install new ventilation via a core vent if there is insufficient ventilation – this needs to be done by the installer prior to them getting on with their main job of filling the cavity with insulation.

Some vents can be blocked with little consequence!

There are types of vent though that are okay to be blocked when cavity wall insulation is installed. There are some vents that are simply there to ventilate the cavity, but obviously when the cavity gets filled with insulation, the ability for air to flow around the cavity is greatly diminished – it is okay for these vents to be blocked.

Likewise, larder vents found in many older properties can safely be blocked – these were commonly found in the kitchen area for preservation of fresh food however most homeowners will have replaced the larder with a modern fridge making this type of vent a little redundant.

Room vents we would recommend to keep open, as they aid ventilation in rooms, which will help avoid the issues highlighted in the opening paragraph, however they can be closed at the customer’s request.

If you feel your home has insufficient vents, or you are worried a vent has been blocked by cavity wall insulation that has been retrofitted within your property – call Extraction4Homes today on 0208 819 9152.

Is your home at risk of damp problems?

Checklist: Is your home at risk of damp problems?

Retro fit cavity wall insulation causing damp is becoming more and more common – you can use the checklist below to assess whether your home could be at risk.

Damp could occur in properties as a result of retro fit cavity wall insulation if there is a combination of these factors:

  • your home is exposed to severe levels of wind-driven rain (zones three or four in our map)
  • your home is located in an unsheltered position, eg not protected by trees or other buildings
  • the external walls are poorly built or maintained with, for example, cracks in the brickwork or rendering.


Published guidance by the Building Research Establishment says that in these cases there is ‘an increased risk of rain penetration if a cavity is fully filled with insulation’. Rain could penetrate the outer wall, bridge the cavity via the insulation material and transfer moisture to internal walls, causing damp.

What kind of damp can affect homes?

There are three main types of damp in the home: condensation, rising damp and penetrating damp

Condensation in the home

Condensation is the most common kind of damp. It is caused by moist air condensing on walls/ceilings and is a problem that mainly occurs during the winter, as at this time of year the external walls are much colder, with the temperature also dropping within the loft area or space – Condensation occurs when large quantities of water vapour from general everyday living becomes trapped within a property. When the warm moist damp air comes into contact with cooler air, or a surface which is at a lower temperature, the result is condensation.


Condensation can be exacerbated by poor ventilation and heating that comes on and off, as this allows warm, damp air to condense. The removal of existing chimneys and fitting air-tight double glazing can reduce ventilation. Make sure trickle vents are in the open position.

trickle vent

Symptoms of condensation include the following:

You may notice water droplets on windows or walls, see dark mould appearing and/or notice an unpleasant smell. If left untreated, condensation can damage paint and plaster and cause window frames to decay.


How to get rid of condensation

On the whole you can improve condensation problems with better ventilation. This can be something as simple as opening windows – in our experience, more than half of those with condensation problems can get this solved by a simple change like this.

Condensation damp is reasonably easy to sort and can often be dealt with by simply opening windows more often, stopping drying clothes indoors, turning your heating on more, fitting new vents or installing new bathroom and kitchen extractor fans.

drying pic

If you don’t have a fan in your bathroom or kitchen, you should consider installing one – these two rooms are responsible for most moisture in the home.

Dehumidifiers can also help, but they are expensive to run, so it is worth getting to the source of the problem before investing.

Rising damp in the home

Rising damp is caused by ground water moving up through a wall via capillary action. Most walls allow some water in, but it’s usually stopped from causing damage by a barrier called a damp-proof course. This is usually a horizontal plastic or slate strip in the wall.

If this is missing or ineffectual, your wall may suffer from rising damp. This type of damp can also happen when the level of the ground outside your home is higher than your damp-proof course, allowing water to get above it.


Symptoms of rising damp

If you have rising damp, you may notice damaged skirting boards and floorboards, crumbling or salt-stained plaster and peeling paint and wallpaper. There may also be a tide mark along the wall.


If your damp-proof course isn’t working effectively, you may need a new one. The most common remedy is for a damp specialist from Extract4homes to drill series holes and inject damp-proof cream, but there may be alternative solutions.

Dig away soil below the level of damp-proof course

If you have a perfectly good damp-proof course (you will need an survey to confirm this), you can solve the problem by digging away the soil on the exterior side of the damp wall to below the level of the damp-proof course. 150mm- 300mm. Back filling with pea shingle for extra drainage.


Penetrating damp in the home

Penetrating damp is caused by water leaking through walls. This type of damp may move around within a building, but this is through horizontal movement rather than by travelling up walls. Penetrating damp is usually caused by structural problems in a building, such as faulty guttering or roofing, cavity bridging or defective insulation.

Symptoms of penetrating damp

Penetrating damp often shows up through damp patches on walls, ceilings or floors, which may darken when it rains. You’re more likely to get penetrating damp if you live in an older building with solid walls, or cavity walls which have retro fit insulation.

Don’t assume your damp problem will always be expensive to solve.  With penetrating damp, something simple such as clearing your gutters can also help.

Is cavity wall insulation suitable for your home?

What is a cavity wall?

A cavity wall is an external wall of a building that consists of two layers separated by an air gap or a cavity.  Masonry (brick or block) cavity wall construction was the most common form of construction for houses built in the UK between 1930 and 1980. However, many other types of construction were also used during this period including 220mm solid brick, timber or steel frame houses as well as concrete system build.

If you can see the brickwork on the outside of the house, look at the pattern of the bricks. If your home has cavity walls, the bricks will usually have a regular pattern like this (or a stretcher bond):

cavity wall pic 1

If your home has solid walls, the bricks will have an alternating pattern like this (this is also called a Flemish bond):

cavity pic 2 solid

How do I know if I have a cavity wall?

If the brickwork has been covered, you can also roughly work out the construction type by simply getting your tape measure out and measuring the width of the wall. If a brick wall is more than 270mm thick then it probably has a cavity; a narrower wall is probably solid. Stone walls may be thicker still but are usually solid.

Sometimes you can see the cavity by looking through the frame of an opening like a window or a door; or you can go up into the loft and look at the way the eaves join to the walls.

If your house is a steel-frame or timber-framed building, or is made from pre-fabricated concrete, different rules apply. A visual check of the loft space is the best and starting point. Retro-fit cavity wall insulation would not be suitable for these construction types.

timber frame pic20150107_112330

Is the home suitable for cavity wall insulation?

Your home will usually be suitable for cavity wall insulation if it meets these criteria:

  • Cavity is clear of any rubble
  • DPC (damp proof course) 200mm-300mm above ground level
  • Your cavity is at least 50mm wide
  • The masonry or brickwork of your property is in good condition
  • The walls are not exposed to driving rain

Remedial works may be required before insulation works can take place. Extract4Homes offers cavity wall clearance for preparation of installation works.


If your property is 10 -15 years old (most houses will have insulation already) please call Extraction4Homes on 0208 8199152 to see if we can help.



Finlock Concrete Gutters

Finlock concrete gutters were very popular back in the sixties  – we come across them every now and then when we survey for cavity wall insulation problems and rarely, if ever, are they found in good working order.

The gutter system is usually known as Finlock. The system comprises an integrated concrete gutter, lintel and eaves product that is fitted in sections. Typically the concrete gutter sections are 200mm to 250mm in width and this incorporates a cavity closure at their head.

The Finlock gutters are fitted to the top of the cavity and the outer face of the wall forming the gutter. A waterproof coating or lining should be applied within the gutter trough before cavity wall insulation is installed. However in many cases this has been overlooked, resulting in issues damage within the cavity wall – normally to the cavity wall insulation.

Problems with Finlock gutters and cavity wall insulation

Having an inadequate number of outlets can cause flooding and leakage. Gutters have often been badly lined or sealed with an asphalt or similar liquid applied product – older repairs very often not only fail but worsen the problems as the finish can be crude and uneven.

Gutters are generally laid level and are consequently extremely liable to blockage and flooding. Over time the sections settle and become misaligned making this situation worse.  As these sections settle, the joints open up and can start to leak within the cavity wall, causing the insulation to become wet.  This leakage can become apparent on the inside of the building with ingress water damage showing. Condensation and dampness become evident internally, typically to the upper 800mm of the wall.

If you have these concrete Finlock gutters in your home and are suffering from damp, please call Extraction4Homes on 0208 8199152 to see if we can help.