My elderly parents' house has an old asphalt roof (30-plus years) which has been leaking for many years. I have done some research and have seen liquid silicone systems. Would any of these be suitable for this type of roof? If not, what would be the best solution?
Firstly, I note the roof has been leaking for many years and thus it is reasonable to assume that the continued water penetration will have given rise to damage to the roof structure. The level of damage will be dependent on the type of structure. Typically, asphalt was laid on a concrete structure on single-storey extensions and, to be fair, there is limited scope for damage to the concrete. However, if the structure is of suspended-timber construction, then there will be a very high risk of decay to the roof timbers and this will need to be investigated further.
A further complication is, given the ongoing leak, it is likely that any decay within the roof structure would be a form of wet rot (due to the amount of moisture) and this tends to be a localised problem. If the roof covering is replaced, thereby eliminating the source of the moisture, the roof will eventually dry out and there is a high risk that the wet rot will “convert” to a form of dry rot and this can be much more problematical for a property, in that it tends to spread more rapidly in search of moisture. Accordingly, given the previous water penetration, it will be necessary to investigate the roof structure with a view to addressing and repairing any damage as a result of the previous leaks.
The other issue to consider is the degree of insulation and ventilation to the roof structure. Given the age (greater than 30 years), it is unlikely there will be any insulation and you should consider taking the opportunity of incorporating insulation within the roof. There are various options for where and how the insulation can be incorporated, for example, under, over or within the roof structure. There are various advantages associated with each option and the decision will have implications on the need or otherwise for ventilation. For example a “warm roof” with the insulation placed on top of the roof structure will not require ventilation whereas if the insulation is located in or below the roof structure, then ventilation will be required.
This then brings us directly to the question of the type of roof covering and the one most suitable for a flat roof. In this respect, there are many different forms of flat-roof coverings including full-bonded flat roofing membranes, loose-lay membranes, liquid silicone systems and metal cladding or linings. All of these coverings, including the liquid silicone system that you refer to, are suitable and there are merits for each solution. If there was a simple one-off answer which suggested that one covering was “the best”, then all the other material manufacturers would eventually go out of business and the best product would always be used.
Clearly this is not the case but it's fair to say that there will be a most appropriate solution when one weighs up all the different factors, including budget constraints. The best way of discovering this is to take a holistic view of the roof with a view to achieving the best combined solution. In this respect, there is no substitute for a well-formed expert view on what is the most appropriate solution in a particular set of circumstances, and your local chartered building surveyor would be well placed to advise you on the best and most practical solution to suit the circumstances. – Val O'Brien
Val O'Brien is a chartered building surveyor and member of the Society of Chartered Surveyors Ireland
