A Guide to the Repair of Historic Roofs - Dublin City Council

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ROOFS A GUIDE TO THE REPAIR OF HISTORIC ROOFSDOWNPIPESDownpipes should be examined for defects, cleaneddown and appropriately refurbished. Replacementsections for broken lengths of downpipe shouldmatch the existing size and profile. Where downpipeshave been partly buried into walls by a coating ofrender they are liable to crack, discharging rainwaterback into the interior of the structure. Spacers shouldbe fitted to ensure that downpipes are properly heldoff the wall, so that if leaks occur the water hassufficient space to run down the back of the pipewithout saturating the wall. Where appropriate, fittinghinged downpipe brackets is very practical as itsimplifies the removal of downpipe for maintenanceor replacement.Cracked or broken rainwater goods can be replacedon a like-for-like basis with half round, box or ogeecast-iron gutter profiles which are readily available.Where castings are more decorative, such as in thiscase, new gutters can be cast to replace the brokensections. Downpipes should be carefully examined,cleaned down and fully refurbished on a regularbasisOverflow pipes can be fitted to hopper heads andcatch pits to alert owners of blockages. Where thegutters are hidden from view, such as secret or valleygutters, this is an especially useful early warningsystem and should be included when any major roofrepair works are undertaken.If there are deficiencies in the design of a rainwaterdisposal system it may, in some cases, be possible toreplace the existing rainwater goods with largersections in similar designs and profile. This may not beappropriate where the existing rainwater goods are ofarchitectural heritage value. Sometimes it may bepossible to increase the number of downpipes servinga roof or to add a new downpipe to a previously unservicedroof area. Depending on the location of theadditional outlet and downpipe, planning permissionmay be necessary for the modification and/or consentfrom adjoining property owners obtained.Some gutters, particularly those with a decorativeprofile, cannot be taken down for repair withoutremoving the lowest course of roof slate. Where suchgutters are cracked or have spots of corrosion, a metalinsert or continuous sleeve can be fitted into thegutter, to cover the faults. The chosen metal shouldnot cause galvanic corrosion. It should be fitted in dryconditions to avoid water being trapped between thetwo surfaces. This repair should suffice until a majorroofing job is undertaken and a permanent repair canbe achieved. For further information see Iron – therepair of wrought and cast ironwork in this AdviceSeries.Having made sure that the method of rainwaterdisposal from the roof is in working order, it isimportant to ensure that downpipes are properly ableto discharge into shores or gullies at the base of thebuilding. The base of the downpipe should notobstruct the grating or impede clearing of the gulley.An unusual example of a decorative cast-iron gutterdetail following the profile of a half-hipped roof71
ROOFS A GUIDE TO THE REPAIR OF HISTORIC ROOFSSECRET GUTTERSSecret gutters are concealed channels which runthrough a roof space to drain into a parapet gutter ora central well, such as where four internal roof slopesconverge to an enclosed area. A secret gutter reliesheavily on the fall of the lead-lined box gutter receiverto work effectively. Because of the inaccessibility of asecret gutter, it is prone to unnoticed blockages. Agrating to prevent bird ingress and blockage fromleaves or debris should be installed and regularmaintenance inspections carried out to ensure thegutter remains free-flowing. The alternative detail ofpiping the secret gutter through the roof should beconsidered if carrying out major roof repairs as itmakes this detail significantly less vulnerable to leakswithin the roof space.Occasionally in terraced buildings, a secret gutter isshared by two adjoining properties and is typicallycarried along the top of the party wall within the atticspace. The party walls in terraced houses were oftennot built up fully to finish beneath the roof slope.Therefore many terraced houses are not fullyseparated or independent in terms of a structural firebreak at roof level. In re-roofing a structure, thecompletion of the party wall to achieve a fire break atroof level should be considered. Where this is desiredthe internal gutter should be re-routed as twoseparate gutters either side of the extended party wallto a detail agreed by both building owners.The term ‘secret gutter’ is also used to describe apartially concealed gutter to the base of an abutmentor gable coping. Where the roof is being re-slated itsprofile will most likely be increased in height by theaddition of new battens, which are thicker than wereformerly used, or counter battens (an additional layerof battens fixed perpendicular to the first layer ofbattens). The relationship between roof covering andcoping upstand may therefore be altered. If there is arisk of water penetration below the lead flashing, arecessed or secret gutter can be formed if the roof iscounter-battened, and an appropriate lead upstandformed to the coping. These works may materiallyaffect the character of the roof, and the architecturalconservation officer in the local authority should beconsulted regarding the necessity of obtainingplanning permission.A lead-lined, secret gutter within the roof space usedto carry rainwater from an internal roof to outfall atthe eavesThe installation of an early warning system in theform of an overflow pipe will alert the owner that thecatchment pit is full and that a blockage in the gutteror hopper head needs to be cleared before excessivedamage occurs72
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A Guide to the Repair of Historic Roofs - Dublin City Council

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