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

More documents

Recommendations

Info

ROOFS A GUIDE TO THE REPAIR OF HISTORIC ROOFSPROPERTY ADDRESS: Furze House PROJECT REF: 312 FHCo. Laois DATE OF SURVEY: November 2007CLIENT’S NAME: SURVEYOR: LELocation of building / roof in relation to main building: Main RoofApproximate date of building:1720-1730s with late-18C addition to south-eastType of roof (e.g. gabled, hipped, etc.):Double ‘ A’ with central valley and hipped endsArea on flat, m²: outer 306 m 2 , valleys 151 m 2Pitch in degrees: 42 degreesArea on plane of slope, m²: outer 412 m 2 , valleys 203 m 2 Rafter size and spacing: 115 x 80 mm @300 mm centresROOF FEATURESRooflights: One access hatch; 2 no. dormersChimneys: 3 no. rendered with concrete caps andto valleys; 10 no. small glass panes light attic spaceornamental pots. Note: valley gutter drains thro’Roof vents: Nonetwo front stacksAbutment / gable: NoneRidge: Dark grey, plain clay ridge tilesValleys: Polymer membrane over timber boarding;Hips: Lead rolls over timber formersdamaged and with inadequate fallsROOF SLOPE & PERIMETER Front, rear & hipped ends: Inner valleys:Original / non-original: Mid-late 20C Possibly originalCondition: OK, but limited life span Bitumen coveredType of slate: Cement, prob. asbestos fibre Natural slateCoursing: 255 mm high x 310 mm wide Varies with random widthSize of slate: 12 x 24” (610 x 305 mm) 12 x 24”Gauge: 250 mm VariesNumber of slates (approx.): 5,500 2,700Colour of slate: Dark grey Grey/blue with green veinTexture of slate: Matt Smooth & finely grainedType of fixing: Galv. nails Wrought iron nailsParging / membrane: Bituminous membrane Lime parging; very looseEaves / parapet detail: Corbelled stone eaves / concrete n/aRainwater goods: Extruded aluminium n/aDIAGRAMAdditional notes:2 no. lead-lined timber box with 1 no. piped secret gutter through roofSample survey sheet for the assessment of roof condition and record of detail47
ROOFS A GUIDE TO THE REPAIR OF HISTORIC ROOFSSURVEY OF ROOF STRUCTUREA survey of the roof should be completed beforecarrying out repair or replacement works. This shouldstart with an assessment of the roof structure:> What is it made of?> Is it structurally stable?> Is it in good condition?> Are there distortions and deflections?The roof profile and the materials used in itsconstruction and covering (including elements such aschimneystacks, roof dormers and lanterns) should berecorded.The cause of any deterioration in condition will needto be determined. Particular attention should be paidto vulnerable areas where water is likely to penetrateinto the interior of the building, for example at theends of the rafters or at the flashings between thegable and the roof slopes and at the base ofchimneystacks. It should also be established whetheror not there is adequate ventilation of the roof timbersand whether fixings are corroded. Checks should bemade for signs of fungal or insect attack in areaswhere ventilation is restricted, such as at rafter ends,behind parapets and around chimneystacks, andwhere pieces of lime parging may have fallen,blocking air flow between the rafters. The opportunityshould be taken to inspect the condition of such itemsas water tanks, access hatches and lights, chimneystacks and aerials, as well as rainwater goods andoutlets. Metal rooflights should be examined for signsof corrosion or distortion and for damaged coverflashings. Similarly, the structural stability ofchimneystacks should be assessed; the capping orflaunching examined for cracks and lifted flashingsreplaced as soon as possible.If the roof covering is to be fully or partially stripped,this provides an opportunity to inspect timbers inusually inaccessible areas around chimneystacks,below parapets and valleys, and along the head of thewall plate where it tends to be warmer and moresusceptible to rot outbreaks.STRUCTURAL APPRAISALIn order to make an informed decision on what repairsare necessary, a detailed survey of individual timbers,their layout, spacing, sizes and condition should becarried out. Once this survey information is gathered, itwill be possible to identify and locate rotten timbersections which need to be supplemented, treated orremoved, and to locate where new timbers need to bescarfed or jointed into the existing structure. The aimof any repair work should always be to retain as muchas possible of the existing historic timber and tosupplement its structural capabilities where necessary.These rafters were originally undersized for theirspan and had deflected, causing slates to lift or slip,and thus allowing water to enter the roof space. Tocorrect the problem, this additional supportstructure was added during roof repair worksIdentifying defectsThe sagging or deflection of a roof should not alwaysbe diagnosed as a roof failure; some unevenness orundulation in an old roof can add to a building’saesthetic and historic character, provided it is not asymptom of ongoing structural instability and is notallowing water to enter the building. However,deflection which has caused the leading edges of theslate to tilt up or protrude is a problem once waterpenetration to the interior roof space occurs. Inextreme cases, roof rafters can deflect to the extent ofstressing the nail fixings and breaking the nail headthrough the slate. Defects of this type should be dealtwith without delay.48
Page 2 and 3: oofsA GUIDE TO THE REPAIR OF HISTOR
Page 5 and 6: ROOFS A GUIDE TO THE REPAIR OF HIST
Page 47: ROOFS A GUIDE TO THE REPAIR OF HIST
Page 99 and 100:
ROOFS A GUIDE TO THE REPAIR OF HIST
Page 101 and 102:
Page 103 and 104:
Page 105 and 106:
Page 107 and 108:
Page 109 and 110:
show all

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

Create successful ePaper yourself

Delete template?

Save as template?