Frequently Asked Questions

To help provide you with more information we’ve compiled this handy list of answers to common questions. Feel free to contact us if you require further details.

How do you insulate suspended timber ground floors?

Devana have developed a unique system for insulating suspended floors. Traditional ground floors have a gap between the timber joists and the ground below to prevent rising damp, with the space ventilated by airbricks in the outside walls. Unfortunately, this makes it very cold and draughty!

We have a very cost effective solution. We can insulate between the floor joists and keep the ventilation below. Our method only needs a few floorboards to be lifted. This makes the process quick and minimises disruption – we can often complete a room in one day. What’s more, because the insulation is blown in, it tightly fills the space between the joists to eliminate cold draughts more effectively than alternatives. For more information and to find out how we could insulate your suspended floor, please contact us.

Can I use cellulose in brick-and-block cavities?

The risk of damage from condensation is too high for us to consider using an organic material between two masonry walls. It is possible for damp to collect in cavities on the inner face of the brickwork. Although cellulose can safely take up and lose high humidity levels, it should not get soaking wet and so needs to be separated by a gap. This makes it ideal for timberframe walls, which have a space between the external weatherproof layer and the frame, but in appropriate for cavity walls which would lose their gap when insulated.

Could I fill my flat roof?

Possibly. Though access to the roof void and the risk of potential problems with condensation make this less likely than with pitched roofs. Materials used for roofs have evolved over recent years and the chances of being able to fill the void are much better with a modern roof, or one that has been reroofed.

The main issue is whether the roof needs ventilation or not. If it has a layer of insulating material above the timbers, it probably will be OK to fill. Moisture is produced inside buildings by general use, and this can be absorbed by ceiling materials and pass through as vapour into the void behind. If the roof is not insulated above the roof timbers, the moisture can condense on the underside of the roof decking. This is not a problem if the void is ventilated and the moisture can be dispersed over time. However, it means we cannot fill the void if it would block the ventilation.

The best way to answer the question is to contact us with as much detail as you can about all the materials in the roof construction, if possible with measurements of each layer. We can analyse the risk of condensation, and calculate the heat benefits of adding insulation. Call us to discuss what information we would need.

Why is airtightness important?

Until recently, builders have not had to try very hard to prevent air/heat leaking through hundreds of tiny gaps in the structure. Now, all new buildings have an airtightness test – an independent tester will fit a fan onto the front door and try to suck the air out of the building. How easy it is to do that is recorded and compared to a target result for each building. Often buildings will fail the test, and that means potentially huge problems trying to find and stop leaks after the building has been finished. Our system of blowing cellulose insulation to tightly fill spaces contributes to airtightness, leading to significantly better test results compared to other insulations.

Is my house at greater risk of fire damage if I use recycled newspaper insulation?

Cellulose fibre insulation is used as a fire retardant material, so your risk of fire damage actually declines if you use cellulose fibre. Studies have been carried out which show it is one of the best insulations to have if you are unlucky enough to have a fire. See Fire Resistance for more info.

Can I install it myself?

Cellulose fibre can be installed as a DIY insulation, and consumer grade material is available in bags which are less compacted so that it is easier to ‘fluff up’ by hand. However, even at the minimum thickness for regulations, this can take quite a long time. Using our system to blow it in is very quick. Other situations, such as walls and closed-in roofs, should be installed by a BBA accredited installer, using the system to achieve a good fill at a good density.

What’s so good about the ‘blown-in’ system?

Two things – it’s very,very quick, and it pumps the insulation into spaces so that they are really well filled at just the right density to work at the optimum performance.

How does cellulose compare with other types of insulation?

There are many types of insulation available. Fibre insulations include cellulose, fibreglass, rockwool, sheepswool, hemp, and others. Petrochemical insulations include polystyrene and PIR foam. Thin multi-layer insulations can occasionally be used in certain situations.

Comparing fibre insulations, the figures used for thermal conductivity of each are quite similar in heatloss calculations to produce U-values. However, in practice, studies have shown that the cellulose system outperforms the others when measuring heat required to get up to temperature and heat retained over time. Only PIR foams can do better in U-value calculations, but have very little thermal mass to retain the heat. Environmentally, PIR foam production is the worst for carbon emissions, whereas cellulose is the best, being actually carbon-negative. More information on the thermal performance of cellulose insulation can be found here.

Is it easy to insulate timber floors upstairs?

Generally yes. Depending on which is more convenient, we can either blow in insulation from above or below.From above,  we can lift a floorboard across the middle of the room, or temporarily cut out a strip if it is chipboard. From below, we can cut circular holes through the ceiling and fix back the cutouts afterwards.Cellulose fibre insulation is very good in floors for both sound and thermal performance, along with fire resistance. It is important, though, to protect inset lights and any heavy-duty electric cables, e.g. shower/cooker cables. Halogen lights burn very hot and should not be tightly covered with any insulation, but all lights should have a ‘hood’ to separate them from the insulation.

How thick should loft insulation be?

In lofts, the current regulations would require at least 250mm. Because it is easy for us to blow more in, we often install 400mm as this is a good way of getting excellent performance for little extra cost.Unlike alternative insulations, cellulose fibre is blown into all the corners and packs tightly around the forest of timber found in most lofts. This makes a very real difference because even tiny gaps leak heat. As an illustration, imagine being in a warm bed on a very cold night – if you lift the covers away from the edge of the bed you can really feel the cold pouring in!

Does it matter if it gets wet?

Cellulose fibre can absorb a lot of moisture without problem, drying out again over time. If it gets really saturated, the weight of water can compact it so that it cannot do its job of insulating. If this happens in a loft, it is easy to pull it out and either shake back some new material or spread some over from around the surrounding area. (Other fibre insulations will also suffer from being saturated). The material is treated against mould, etc.

Is it dangerous in any way?

Cellulose fibre is not dangerous, indeed it is very difficult to come to harm with this material. Our installers, who work with cellulose fibre all day, are safe to work without masks. We do, however, recommend using one in confined lofts simply because it can be more comfortable. If anyone were to try to eat it, a harmful amount would be many times more than it is possible to eat! By comparison, mineral fibres (rockwool and glassfibre) and PIR foams, are universally unpopular because they are so itchy and irritating in the throat. Cellulose is much more friendly!

About Devana

We are specialist installers of cellulose fibre insulation, installing all over the country from our Cambridgeshire base.

With a wealth of experience covering insulation, building and design; we would love to find out how we can help with your project.

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Devana Insulation Limited 
81A Fred Dannatt Road
IP29 7RD

01638 501069

Retrovive Floor

Retrovive Floor is the only system that can install insulation underneath your traditional suspended wooden ground floor WITHOUT taking up all the floorboards.

Visit our Retrovive Floor website for details.