COMMON ROOFING DEFECTS
your surveyor need to be alert for clues to past problems, such as tell-tale brown water staining on internal surfaces. Running a damp meter over the upper walls can also help pinpoint hidden leaks. Even where a roof appears to be perfectly sound at first glance, an experienced eye can often detect weak points with potential to morph into expensive problems in the future.
Here are some of the most common roofing defects and repairs, to help you weigh the job at hand.
1 LEAKS AT FLASHINGS AND VALLEYS
The most common roofing problems are related to small leaks at junctions with walls and adjoining roofs etc. But anything that projects through a roof slope, such as a chimney stack or soil pipe, creates a potential vulnerability which will normally need to be protected with a suitable seal or flashing. Valleys, where two adjoining roofs meet, are another common weak point. An example of this is where main roofs abut bays, gables and extensions.
Where decent quality lead flashings have been used to seal junctions they’re normally very durable, although with age they sometimes crack or come loose and need re-fixing. Classic botched repairs to look out for are short-life DIY flashing tapes, or where old defective flashings have been painted to temporarily seal a leak.where cheap cement mortar ‘fillets’ have been used instead of metal flashings, they are notoriously prone to cracking. Any resulting leaks and damp patches can
‘‘ The most worrying cause of roofs sagging is where supporting roof timbers have been cut away for illegal DIY loft conversions
often be detected in lofts, or further down on bedroom ceilings, walls and chimney breasts. The good news is it’s unusual for roof timbers to succumb to rot as long as the roof spaces below are kept well ventilated. But where any timber decay is evident, the affected areas will need to be cut out and replaced.
Defective old flashings should be replaced with new leadwork (of a minimum thickness Code 4). But where a flashing has simply come loose it may only require localised re-fixing into a new mortar joint.
Valleys can be re-lined using pre-formed valley trays of GRP (glass reinforced polyester). However with older roofs replacing traditional leadwork with matching new materials is the best policy. Victorian hipped roofs often have hip roll joints in lead or zinc and these sometimes need repair or replacement.
2 DEFECTIVE POINTING
Surveyors routinely flag up eroded mortar joints to the ridge tiles along the top of the roof (as well as on hipped roofs). Erosion is also fairly common on pointing on the verges at the sides of gable roofs where the tiles project out slightly. If neglected for too long there’s a risk of tiles coming loose in storm conditions, potentially risking serious injury. Fortunately, these sorts of defects are fairly straightforward to repair apart from the need for access at height. So any areas where mortar has significantly eroded should be repointed and any loose ridge tiles secured and re-bedded.
3 SLIPPED OR MISSING TILES
The occasional slipped tile is fairly common and is rarely a problem. Traditional slates and plain tiles are laid so they overlap with two or three layers at any given point. This means that any small gaps here and there shouldn’t let the rain in (except perhaps in storm conditions) because there’s another layer underneath. Most roofs will also have sheets of underlay
beneath the tiles so that any rain that does find its way through should safely disperse down to the gutters. However most older roofs (pre 1950s) weren’t originally provided with underlay, instead relying on a brisk flow of air ventilating the loft to dispel any moisture. Nonetheless, in roofs without underlay or where it’s badly torn there’s a greater risk of rain penetration, so there’s greater urgency to fix any slipped or missing tiles.there’s also more risk of rain getting in where roofs are clad with larger interlocking tiles which have less overlap between courses.
Over time, tiles can eventually start to develop defects such as broken ‘nibs’ (the supporting lugs that clip over the roof battens). Traditional clay tiles have a longer lifespan than the cheaper concrete varieties but even these can eventually start to erode and break. But roof coverings of all types sometimes get dislodged in severe storms and small gaps can develop as they adjust to timber roof structures settling over time.
Replacing individual tiles is normally straightforward as most aren’t nailed in place so can be lifted with a trowel allowing a matching replacement to be eased underneath and hooked over the batten.
Shallow pitched roofs clad with large interlocking tiles (common on 1970s properties) sometimes develop problems on lower roof slopes near the eaves if the underfelt has sagged, diverting rainwater down cavities in the walls.this requires the lower layers of underfelt to be replaced, before re-battening and replacing the tiles.
Natural slates are far more brittle than tiles and readily crack if mistreated or walked on without protection (e.g. to install TV satellite dishes). Good quality slates can last 150 years or more but eventually start to de-laminate in layers.the most common cause of slates slipping is rusted fixing nails but because each slate is nailed to a batten, and slates vary in size, they are much more difficult to lift out and replace than tiles.the standard method for securing the occasional loose slate is with small metal clips known as ‘tingles’.
‘‘ Rather like people of a certain age, old roofs can sometimes be prone to sagging
4 COMPLETE RE-ROOFING
Where you can see more than about four or five slipped or missing tiles or slates on a single roof slope, it’s likely to indicate that the roof coverings are nearing the end of their useful life and will need stripping and re-covering in the not too distant future.
One simple clue to whether the original roof coverings may soon need replacement is to take a look at similar roofs in the street to see if many have been re-clad. That said, it’s not unknown for homeowners to be talked into unnecessarily re-roofing; which brings to mind the case of a friend’s Victorian house in London where the firm undertaking the loft conversion persuaded him to pay for the perfectly sound original Welsh slates to be replaced with cheaper modern artificial replicas (the contractor artfully salvaging the originals for re-sale!).
Artificial slate can be a perfectly good budget-priced substitute for the
real thing where old coverings are genuinely in need of replacement. But the lifespan of traditional natural roof coverings is generally far superior to later manufactured materials. Handmade clay tiles or stone slates can last over 250 years compared to only around 70 for most types of concrete tile.
In older roofs the undersides of slates and tiles in the loft can be checked for signs of softening, flaking, or white powdery salts indicative of porosity; once water starts to be absorbed by porous slates or tiles it they can become vulnerable to freezing which eventually blows them apart.
Some things look much worse than they actually are; for example, moss on roofs is quite common but in itself isn’t normally problematic other than looking unsightly and potentially blocking gutters, and can be professionally jet washed if required.
SAGGING ROOF SLOPES
Rather like people of a certain age, old roofs can sometimes be prone to sagging. This is often the result of the timber roof structure settling over time, while the adjoining masonry gable end or party walls retain their erect stature creating an undulating roofscape. Old roofs sometimes also ‘dish’ where the supporting internal walls have settled over time.
More serious bowing inwards can sometimes be due to the original lightweight slate roofs having been re-clad with heavier modern concrete tiles without the supporting roof structure being beefed up first. Similar symptoms can be the result of ‘roof spread’ where the rafters have pushed out the upper walls.
The most worrying cause of roofs sagging, however, is where supporting roof timbers have been incompetently cut away, for illegal DIY ‘loft conversions’, botched installations of roof windows, or just to make more space in the loft. More rarely, movement may be the result of localised timber decay.
In severe cases remedial structural work may be needed and a structural engineer should be consulted. But where the roof structure is satisfactory and there’s no leakage, a fair amount of historic settlement can be perfectly acceptable.
Overloaded, spread or weakened roofs can normally be stabilised by installing additional purlins and struts or collars to improve support to the rafters. This is fairly simple carpentry and shouldn’t be too expensive.
COSTS FOR ROOF REPAIR WORK
Prices for roof work vary enormously depending on geographical location, complexity of the roof, ease of access and the extent of work required — which may not always be immediately obvious looking from ground level. Most roofers charge around £200 to £300 per day for labour.