Glass roof repair
Insulated glass roofs considerations
When homeowners shop for new solariums or sunrooms, the most sought after option is a glass roof. The notion of bird watching in the day and star gazing at night is almost poetic. However, reality gets in the way.
There are three considerations that are often overlooked:
Looks – in summer, insects find their eternal resting place on roofs. Canada geese leave their mark. Fall and spring bring twigs, leaves and buds. Winter’s snow covers the roof altogether. The same is true for a solid roof, but then none of it is visible.
Winter heat loss – the best glass roof conducts cold more than a solid insulated roof. As such, you would pay to heat the sky above.
Summer heat gain – in theory insulated glass roof protects against heat. In reality, it does little in direct sunlight. Sunrooms are rendered unlivable without sheds – it becomes a sauna.
Technical – concerns that are specific to traditional glass roofs:
Expansion – glass roofs have to be sealed to perfection. An overlapping roof – meaning any other roof – rests above the rafters, glass panes rest in between. Plate glass expansion coefficient is different to wood or aluminium – 5, 2-3 and 12 respectively, so between summer’s +30°C and winter’s -20°C the disproportional shift will crack any applied sealant.
Edge ice dam – as noted above, a typical roof glass panel is installed lower than the rafters or the stops (the wood or aluminium strips holding it in place). Adding to that, heat escape through the slightest glass shift which will cause inevitable ice build-up at the low end of the roof.
Poor drainage– a concern associated chiefly with wood structures. Where the glass shifts, a small gap collects water that later freezes and pushes the pane back. This creates a cycle that results in water build-up between the wood frame and glass unit. Now, two things happen:
– the edge of the sealed unit sits in a bath of water, causing a premature seal failure, leading to costly glass replacement.
– water build-up with no drainage will eventually rot the wood beams and rafters. We have seen cavities as big as an adult’s fist. In this case not only the glass needs replacing, but the wood structure as well.
Glass roof repairs
When failed glass roofs need replacement, the first resort is the original supplier. In theory, it should be under the promised lifetime warranty, in reality, the fine print kicks in. Furthermore, companies that have ample product failures tend to fail and fade away themselves, so no comfort there. Moreover, home owners who bought the house with the glass roof already installed have no knowledge of who the manufacturers / suppliers are.
Home owners first request is ‘to seal the leaks’. There is no practical way to do so. A fresh sealant layer can not be applied over an existing one. All have to be cleaned and then re-sealed. This may work for one year, but since it is superficial treatment only a fresh leak will re-appear again after the next freeze / thaw cycle. But, now the contractor who attempted the repair is held responsible – ‘own the roof’.
The only real way to rectify the problem is to remove all capping / flashing, sealants, uninstall glass, clean all seats and re-install glass units properly. However:
As stated above, it is most likely that the glass sits in a puddle of water. When the sealed unit is removed it would break apart – two layers of glass and a spacer. There is no way to put it together again – a fresh sealed glass needs to be ordered. The new unit has to be tempered or laminated, so it may take 2-3 weeks, meanwhile, the old glass has to be temporarily re-installed and sealed.
This will not prevent the unit installed next to it to fail later, so it is wise to redo the whole roof at once. It works out cheaper and ensures peace of mind for a couple of decades, instead of getting through the repair cycle every other year.
Glass installation process
When glass had been initially installed, different sealing modes could have been used. What we see most is either a silicon bead on top and bottom or butyl glazing tape on the bottom and a silicon bead on top. Neither is proven to perform for the long term.
If sealed with silicon only, glass shift will tear the sealant bead and let water in and air out. The right way is to use butyl tape top and bottom. This type of glazing tape is made of a rubbery material, black or grey, with strong adhesives on both sides. It is used to seal glass while being flexible enough to absorb slight structural movements. However, butyl tape is made to perform while glass is vertical, meaning no pressure on the tape itself. In roof application, the heavy sealed glass units rest on the tape, so after a while, the tape will compress – and the whole unit would shift down and leaks appear.
What we use for the same application is a commercial-grade tape, specifically made for pressure application. The base tape is similar to the regular tape, but inside runs a continuous EDPM shim to keep it from compressing. It is a costly solution, but it lasts.
After the glass units are in place, the top is sealed with a conventional glazing tape, stops applied, capped and sealed again.
All above is good if the roof structure is aluminium. If the roof is held by the wood structure it may be worse, if the wood is damaged. There are telltale signs, but in most cases, we cannot judge whether the wood is rotten or not until the glass is removed. If the structure is repairable, new wood sections are milled on-site and re-installed If damage is beyond repair, or where individual joists are compromised, repair may take longer. Needless to say, that should repair not be completed on the same day, all openings are covered for the night.
Rotten wood fascia.
Water seeps down to bottom of wall.
Rotten fascia removed.
New wood implant.
Rotted inside corner.
Butchered previous repair attempt.
Butyl glazing tape.
Glass pane with mounted glazing tape.
Tape simulation – shim shown on bottom.
Simulation of glazed roof – left side as installed, right side after a decade.
Front beam simulation – glazing at installation time.
Front beam simulation – once water gets in.
As above, demonstrating warm air leak creating ice dam.
Correct glass panels installation
Simulated aluminum roof joists.
Gasket detail of above.
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