September 1, 2022

Monitoring to extend lifespan of roof constructions

Monitoring to extend lifespan of roof constructions

This article was first published on Bolius as part of their mailbox answered by impartial experts.

According to the maintenance plan, the roof must be replaced now, but according to my own environmental awareness the roof can last longer - can monitoring with a sensor system extend the life of the roof?

Hi Bolius

We have had a condition report prepared for our property (24 condominiums) from 1904. As with the last report 11 years ago, the architect (same as last time), refers to our asbestos roofs on the side-buildings as “old”, “worn”, “repaired” and “moss overgrown”, and that we should consider replacing it. This is a classic Copenhagen roof: Eternit on the sloping surface, roofing felt on the flatter surface. Please see attached picture with markings.

The arguments “old”, “repaired” and “mossy” do not in themselves appear to be valid reasons for replacement. “Worn” may be a valid cause, but what does it really mean? And what will one have to look for in order to anticipate an imminent issue?

Will you be able to see the wear from the inside? Are there scientific methods for predicting when roof construction and roofing materials will no longer fulfill their purpose?

Could an alternative to replacement be extending the life of the roof by installing a sensor system that can continuously monitor the roof’s ability to keep water out? Do such systems exist?

When I ask, it’s not because I want to rule out that we should change the roof, but because there seems to be a prevailing tendency for everything to just be replaced “for the sake of good order and peace of mind” - even though spot repairs can have the same effect and will be able to make up for a fraction of the price. Likewise, it is not because you are secured against a mounting fault and the like, during a replacement of the roof, where the result can thus be the opposite of the intended.

As mentioned, our architect argued that the roof should be replaced 11 years ago, but we chose not to do so at the time (the roofing felt was changed, however), and we have not experienced any issues with it in the intervening period.

Best regards


roof construction

Bolius responds

Hi Henrik

As an expert in constructions, who also makes a lot of maintenance plans, I know this issue very well.

One can easily come to the conclusion that the roof is worn and old, and then later read an earlier report (maybe even one’s own) and see that the same exact thing was said 10 years ago.

But when it comes to maintenance, I always say that it is best to prevent and change things BEFORE it goes awry! But apart from that, I completely understand your thoughts and assessments.

Eternit decomposes slowly but surely, and in addition to being able to crack (and thus become leaky), they can also become so porous that they are moistened throughout. As the moisture passes through, it begins to affect the battens they lie on, along with the roof space itself. Thus, in addition to rot and fungus in the battens, mold growth can occur.

Moss (it takes more than what I can see in the attached picture) can lift the slabs a bit. If there is very heavy moss, the moss pads can lift so much that the plate breaks, and in addition, larger layers of moss can hold onto the moisture, which in turn breaks down the slate.

If the slate slabs are completely moistened, they can get frost damage by prolonged frost. So you have to keep an eye on your roof, and that is earlier said than done with this type of property.

However, you can mount an automatic moisture meter on the back of the roof, for example on a batten, which can then provide you with a notification should it detect moisture. It could be a wireless moisture sensor as the one from Woodsense.

That is pretty smart.

Best regards

Morten Mathiasen

Morten Mathiasen

Construction engineer, Energy consultant

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