Which is your preferred insulation for a building? My bet is your answer is spray foam insulation. This is the likely answer you will get from many people. I mean, who wouldn’t like an insulation that is so easy to use and has been used for decades. It can be sprayed on most surfaces, can penetrate in tight spaces, and also provides good insulation. In fact, statistics show that spray foam is preferred over fiberglass batt and other insulation types. You can choose either the open or closed cell varieties, both of which provide insulation and an air barrier as well. But, did you know that many experts, including ourselves, don’t recommend this insulation type? Knowing the question is likely to come next, let’s shed light on why we don’t advocate for this type of insulation.

1. The Insulation is Rather Thin

Have you ever looked at the thickness or density of the spray foam inside your walls, partition or under the roofing?

Compared to other alternatives, spray foam is relatively thin. The main culprit here is the closed cell foam which is a bit challenging to install compared to open cell type. Usually, the contractor will spray 2 inches in walls while the rooflines will get about 3 inches of foam. This is seen as sufficient to meet the energy code regulations as well as offer good insulation. However, a closer look at the end product or houses that have this type of insulation shows that in many cases, the insulation doesn’t achieve the desired thickness or it varies from one point to another. In many instances, the appearance will be very bumpy and this means that some sections will lack or have poor insulation.

2. Spray Foam Pulls Away

Spray foam is designed to maintain contact with the surfaces so as to offer the best insulation. This also helps create a nice airtight envelope. However, research shows that there are many cases where the foam pulled away from the partition, wall, rooflines and other areas. This happened without the consumer knowing and was discovered by an expert during an investigation. This problem mainly affected closed cell foam although it can still affect open cell foam. Experts and contractors normally blame this on poor mixing of the compounds, spraying the foam while the temperatures are high, oily and dirty surfaces or low-quality chemicals. While the uninsulated area may look small, the thermal inefficiency (heat gain or heat loss) may be high.

3. Prone to Air Leakage 

Spray foam serves as both the insulation and air barrier, and for it to offer the best thermal properties, both have to be balanced. Unfortunately, this is at times hard to achieve especially even working on tight angles or restricted spaces such as attics or lofts. An installer will miss a spot; others will spray very little foam increasing the chances of air leakage. While spray foam proponents use the air sealing capability as a key selling point, truth is that unless the product comes in contact with the targeted surface, this benefit won’t be realized. Sadly, many people only realize the oversight when problems arise later and after having to foot high energy bills.

4. Creating an Envelope is a Challenge

The secret to ensuring the home or any other property is well-insulated lies in creating the perfect envelope. This ensures there are a good barrier and no air leak. However, it’s not really easy to know whether you have sprayed the right amount especially in a closed cell type of insulation. There is the likelihood of using too much or too little, both of which have negative impacts in regard to thermal properties. It’s also possible to miss the small and tight spaces and this will allow in heat or cold or serve as an escape point. This problem is commonly seen with odd-shaped or very narrow roofs.

5. All Future Repairs To Roof Tiles Becomes Impossible

If you arent concerned about any of the reasons not to choose foam insulation above, this is the one problem which means we do not recommend foam insulation sprayed underneath roof tiles at all! As soon as this is applied to your tiles from the underneath you make any future repair work on the roof almost impossible. So if in 5 years time the foam was not doing its job the whole roof would have to come off to fix the problem. Your tiles become “cemented” to the trusses and the rafters so can not be lifted off and replaced.

This is obviously a hugely costly reason as to why you should stay away from spray foam roofing insulation


There you go- some reasons that make spray foam, not the best option. While it does have good thermal and insulation properties, it still comes with many shortcomings as indicated above. Unfortunately, a consumer will know of the problems many years later. This will come in form of heat gain, heat loss, or high energy costs. And to correct the problem the home will have to be redone again at an extra cost. You can nonetheless prevent such issues by dealing with an experienced, reputable and well-known contractor. Such a firm is more likely aware of the downsides of spray foam and will have put corrective measures or alternatives in place. In addition to guaranteeing you of quality and unmatched insulation, you also get peace-of-mind.

Roofer Plymouth 01752 967500

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