18 September 2010 Register  Login
Roofs and Roof Drainage

Its ROOF is arguably the most important part of your church building. Keeping it in good condition, together with the gutters and downpipes, should be your first priority. Failure to do so will entail vastly more expense than undertaking quick and effective repair and could eventually threaten the future of the whole building.

ROOF COVERINGS

Pitched Roofs feature on the great majority of Scottish churches built before the mid 20th Century. Slate is the usual finish, originally coming mainly from Scottish quarries but more recently sourced from Wales and the north-west of England. It comes in small units which need to be overlapped to keep out the rain and snow. To make economic use of varying sizes from the quarry it is often laid, to pleasing effect, in courses which diminish upwards towards the ridge.

Slates are drilled at the top or sides and then traditionally fixed by nails to underlying timber boarding (sarking). Failure of the nails can cause the slates to slip out of place (nailsickness). Where this is persistent and severe it will normally be necessary to remove and replace the slates over that entire roof slope. Sometimes the sarking will need replacing as well. In that case not all the slates will be capable of reuse and the rest will have to come from elsewhere, possibly taking matching replacements from a less conspicuous part of the roof.

The only Scottish slates now available will be second-hand and they are in short supply. An experienced slater, taking advice if necessary from a specialised architect or surveyor, should be able to obtain matching natural slate from these and other sources. Burlington  slate from the north of England is often a good match.

Note that much imported slate is inferior in quality and life expectancy to that from British quarries. Obtain experienced advice before using it.

It is also important to ensure that non-rusting galvanised, stainless steel or copper nails are used in slating repair.
And never allow bitumen paint or other such 'remedies' to be applied  to seal a nailsick roof. It will prevent the gentle natural ventilation needed by the structure below and make the slates incapable of reuse.

TILED ROOFS feature less frequently on Scottish churches.

Pantiles, traditionally used on older houses and farm buildings in the east of Scotland, have rarely been employed in church building. Plain pink Rosemary hand-made clay tiles, however, were specified by many church architects in the late 19th and earlier 20th Century and are still manufactured today. They are usually fixed with nails, like slates.

Concrete Tiles and other machine-made products will not normally make satisfactory substitutes for these traditional types. Apart from looking inferior they are likely to be considerably heavier and thus liable to overload and stress the structure below.

Whether your church roof is slated or tiled, however, you should always procure replacements as close as possible in colour, texture, thickness and size.

CORRUGATED IRON

Some Scottish churches have been erected economically in prefabricated sections covered with this material. Dating from the later 19th and earlier 20th centuries, they mostly survive in remoter country areas. It is vulnerable to pitting and corrosion if left unpainted and to loosening of fixings and flashings. Keep it regularly painted, ensuring that the fixings are intact and that the flashing remains flush with the profile of the sheeting.

OTHER METAL FINISHES.
Lead     Copper   Zinc       see  FLAT ROOFS.

FLASHING describes the flexible material, usually metal, which is laid to prevent water from penetrating the joints between roof surfaces and upstanding features such as chimneys and skylights. Lead flashing comes in various thicknesses or codes. Code 5, being more flexible, is commonly used for this purpose with heavier grades being specified for other roofing work. Metal flashing is also carried out in Zinc and Copper.
 
Non-metallic flashings in mineral felt strips, pitch and artificial composite products will not be so durable. However all forms of flashing are prone to eventual failure by pitting or cracking and they can be displaced in severe weather.  Inspect for security after storms and when any high level work is required. Flashband  tape can safely be used for emergency repair and should be replaced by more permanent flashing within 6 months.

RIDGING is similar in purpose, comprising specially shaped tile or metal units protecting the apex of a pitched roof from water penetration. Being exposed, these ridges are also vulnerable to high winds and they should regularly be checked by eye for integrity. At the same time, make sure that the clips attaching metal ridging are all still in place.

UNDERLYING STRUCTURAL ELEMENTS  normally comprise Roof Trusses, some simple, others more sophisticated, supporting lighter timber framing which in turn supports the 'sarking' mentioned above. In very simple buildings and in some where elaborately carved trusses are designed to enhance the church interior this structure may be exposed to view from below but more often it will be concealed above a ceiling.

The ends of the trusses will be seated on or near the wallheads, protected by the edges of the roof and the gutters, and so will be affected by any lack of proper maintenance. Wet or dry rot problems then commonly ensue with costly demands on fabric maintenance funds even if cured without  long delay. Where truss ends rest on corbels, watch for drips caused by an unseen roof leak overhead. It is known for water to collect here and to start to rot the timber.

FLAT ROOFS suited to our climate are not laid strictly level, being designed to slope gently towards guttering or rainwater outlets. On older church buildings they will normally appear only as part of later extensions. From the mid-20th Century  to the present day, however, they have become commonplace as part of the general changes in architectural practice and fashion dictated by new structural possibilities and the arrival of new materials.

ROOF FINISHES  in higher quality work will be metallic - Lead, Zinc, Copper or Coated Steel.
Cheaper construction will  rely on mineral felt, sometimes surfaced with stone chippings, or asphalt. These roof surfaces have shorter lives and are prone to cracking with age and where this combines with pools of water caused by faulty drainage, water will be bound to penetrate.

Do not expect continuous patching of felt to be worthwhile. Total renewal will be needed sooner rather than later and it may be worth considering replacement with a more durable material, only using a 'breathable' underlay. Metal roofs, notably those formed in lead, will expand and contract according to temperature. This will also vary with the length of sheet used between expansion joints. Metals that have suffered only local damage should only need the replacement of individual sheets.

Lead roofs, normally formed in  the thicker grades, will  last for generations but are nevertheless vulnerable to puncture, for example by heavy footwear. It is thus good practice to put down duckboards for use when necessary and to lay them also over wider lead gutters. Laid in longer sheets or on steeper slopes, lead may also have a shorter life.

A lead roof can be patched on the spot by 'burning' but cracks and leaks will usually mean that the time has come to renew it.

The life expectancy in years of these roof finishes is roughly as follows:
Mineral Felt  15
Asphalt  20-40
Zinc  50
Copper  80
Lead 100-150

And always when you suspect that water may have penetrated a flat roof and arrange for the repair of the covering, ensure that the structure below is always checked for possible rot damage before the job is finished.

Further information can be found on these websites of the respective Manufacturers' Associations.
                                                                                                            
GETTING RID OF THE RAIN
In early times many roofs were built with overhangs to let the rain drip straight to the ground. Today rainwater is collected and directed downwards via the familiar system of gutters and downpipes known collectively as rainwater goods.

GUTTERING
Eaves Gutters consist of long sections of channelling attached by brackets to the building. Traditionally they are formed in cast iron, modern alternatives being aluminium or heavy duty plastic. Cast Iron left unpainted will rust over time but it is essentially a long-life material particularly sympathetic to the character of older buildings. It is vital to ensure that the joints between the gutter lengths remain well sealed, that the fixing brackets are rust-free and secure and that no slippage or blockage has affected the intended flow of water into the outlets. 

Parapet or ''Secret' gutters lie behind walls raised above the level of the eaves and thus are normally invisible from ground level.They do not rely on ready-made components and are usually made on site by forming a metal lining, typically of lead, over timber boarding. Faults will not necessarily be as obvious as those affecting eaves gutters which can be inspected from the ground, making regular checking all the more important to make sure that they are free of rubbish and any pooling of standing water. Most such gutters, however, have a visible overflow  which, when dripping, will  indicate any blockage.

This advice applies equally to Valley Gutters and any similar hard-to see metal lining found between adjoining roof pitches.

Gutter outlets must likewise remain completely clear and it is strongly recommended to fit them with stainless steel or other non-rusting 'birdcage' mesh  to prevent debris blocking the pipework below.

The incline of every gutter must remain adequate, something not always possible to judge when dry. It is better, therefore, to check this during rain or by using a hose, at the same time ensuring that the stop ends beyond the outlet are in good condition.
                                                                                                                      
DOWNPIPES complete the process of safely removing external water from the building fabric. They may be attached to the exterior or concealed internally, sometimes working as an integral part of a structural system of metal columns within the building. The transfer of water from the gutters is sometimes assisted by hopperheads of greater size which can be attractively ornamental and demand the same degree of maintenance.

Cast Iron is the best choice of  material for long-term duty if painted regularly, including parts not readily visible. Cast Aluminium is also now in common use but can be affected by atmospheric pollution. It should also be painted as protection as well as to make its shiny surface less conspicuous.

Plastic fittings are to be avoided.  Their permanence is untested and, particularly where your building has any historical merit, they are likely to be out of sympathy with the building's character.

When inspecting external pipework, note the condition of the clips holding it back to the wall which should remain well painted and rust free.

It is not always easy to check behind pipework and a good tip is to use a hand mirror for this purpose.

Other useful advice: To test if an iron downpipe is clear, see if it rings true when struck. When a pipe which runs straight to ground is blocked and cannot be easily cleared, it is better to break a length and to replace it soon than to leave the problem to get worse.

Internal Downpipes are usually  much more difficult to monitor and access and if it is possible to replace them with an external system this may be well worth considering.

As general advice, it is always best to check for leaky rainwater goods when it is raining hard and any drips and blockages will be most easily apparent. Overflowing gutters are an obvious sign of weakness as is water running down the outside of pipework or adjoining walls. Also look for possible signs of trouble when snow is melting fast.
At other times, signs of green or other dark staining and streaking on nearby parts of the fabric will surely indicate that rainwater is not escaping to the ground as intended, the most likely cause being some fault with the rainwater goods.

It is essential to walk around your building regularly, on the lookout for just such signs and to move fast in dealing with the trouble.

To follow advice about drainage at the foot of your building, go to the section on WALLS.

  

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