This post is primarily relevant to older buildings – say late victorian to mid sixties – earlier than this and all sorts of interesting timbers are often added and after this roofs are very often of prefabricated timber trusses. [oh and a quick rear end cover – this is not, and not intended to be, comprehensive]
The first thing we look for are a good sized loft hatch allowing access into the roof space or roof spaces, sometimes that means that two hatches are required if there is a rear addition roof. A small head and shoulders hatch will do but is a challenge for the ample surveyor….
A check of the hatch needs to be made to make sure that it is properly trimmed – it’s no good just to cut a hole through roof timbers and hope for the best, any cut through a joist should be trimmed with at least one and ideally a pair of similar trimmers transferring load to adjacent joists.
If there is a loft ladder it should be properly installed, have working safety catches and importantly be the right length – you would be surprised at the number of ladders we see that are too short and consequently are too steep.
If there’s no light then it would be good to provide one or to put a light on an extension lead. So with a hatch, a ladder and a light we can start to look at the roof structure –
We expect to see rafters – they’re the sloping ones, and joists – the flat ones usually supporting the ceilings below. About halfway up the rafters there will almost certainly be purlins running perpendicular to the rafters and probably a series of struts supporting the rafters and transferring loads to the partitions below. Sometimes there will be collars or horizontal ties between the rafters to triangulate the structure like a capital “A”.
So, assuming all those timbers are in place they need to be checked for defects – a few splits are usually OK but if they’ve broken then there’s a problem, the foot of the rafter needs to be checked to see if it has moved outwards [roof spread, often limited by the collars], the purlins need to be checked for deflection or bowing.
Roof spread and bowing timbers can be indicative of overloading so a check needs to be made to conform whether the roof covering has been changed – concrete tiles are very much heavier than slate for instance. If there has been a change in covering extra strengthening timbers may be needed – possibly extra struts and collars.
While we look at the timbers we need to inspect the joints and make sure they’re well detailed, at the same time we’ll keep an eye out for woodworm holes and any decay – more often than not wormholes go way back and are not current – we’ll check for the distinctive frass which can indicate recent activity. Its worth noting that many roofs have had “precautionary” timber treatment over the last 20 years, more often than not several times as buyers get it done just in case because the mortgage valuation told them to!
So assuming the timbers are OK then there are the other bits and pieces – is the roof insulated, if so by how much? These days we’re looking for at least 250mm between and over the joists, if it’s only 100mm or so then it should be upgraded. Older insulation such as wood shavings should be removed as shoudl hoegronwe soilutyions such as shredded newspaper . Oh, and the back of the loft hatch should be insulated too.
What condition is the party wall in? If there isn’t one then one will need to be built to ensure there is fire separation between the houses, any holes in the party wall should also be infilled.
Under the tiles or slates but above the rafters there should be some form of underfelt, if there isn’t then it’s an indicator that he roof covering is a good age if not original. Coverings have a variable life span but typically 70 to 90 years is about the maximum.
Finally we’ll have a look to see if there is any cross ventilation – either original or later and check for any dampness below chimney stack flashings and the like.
What we don’t want to see is no insulation, loose boards randomly laid over joists, polythene, cardboard, hardboard or even old carpet nailed or stapled to the underside of the rafters.
You could of course use the above guide to check and survey the roof yourself or alternatively you could employ an experienced and competent surveyor to do it for you….!