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Inside an Historic Roof

Information Inside an Historic Roof
Inside an Historic Roof - Nicholson Price Associates

There are some parts of a building survey that I look forward to, but crawling around in a roof space is definitely not one of them.

The roof space is normally referred to in the UK as a loft, attic or very occasionally a garret. All three terms tend to be used to describe the area enclosed by the roof slopes but for the purposes of this article, a loft is normally a storage area accessed by some sort of hatch, an attic or garret is a room formed within the roof space and accessed by a staircase.

Discovering that the property to be inspected has attic rooms open to the ridge and that they are accessed by a nice safe staircase immediately endears me to the property. Don’t get me wrong, if there is a loft to be inspected I will thoroughly inspect it, but the process is often at best unpleasant, and at worst downright dangerous.

Heights don’t bother me, I’ve walked along unguarded castle roofs, tiptoed along church parapets and clambered through hugely heavy cast-iron roof windows to get a better look at a lightning conductor or a suspicious looking lead gutter.

The initial problem is normally the height and position of the loft access. Why someone would decide to construct a loft hatch not much bigger than a table mat and place it perilously close to an open well staircase never ceases to amaze and annoy me. This seems to be particularly prevalent in Victorian buildings with 12 feet high ceilings which means my telescopic ladder will just about reach the opening at a near vertical angle. Occasionally the owners have installed a pulldown ladder but this seems to be very much the exception.

Mid 19c Barrel Ceiling - Nicholson Price Associates

MID NINETEENTH CENTURY BARREL CEILINGS BELOW

Teetering at the top of the ladder I normally pause to consider whether the staircase well is wide enough to allow me to fall all the way to the ground floor, or whether I might get lucky and merely bounce of the balustrade with a few broken ribs and a ruptured spleen. Pushing the hatch out of the way normally involves a torrent of expletives and a considerable physical struggle especially when there is a suitcase full of Christmas decorations and a couple of broken bricks sitting on top of it. Why! By this point in the proceedings, my stress levels are at DEFCON 1 and I am seriously considering a change of career.

Bear in mind that it’s not just me that has to squeeze through the hatch, I also have a number of accoutrements which are required to complete the inspection, all of which have to be pulled up on a rope. Once I’m safely inside the loft I start by removing the insect parts from my eye’s, and the assorted cobwebs and other detritus from my hair. There are lots of ways to die or render yourself seriously unwell in an old loft; uninsulated electrical cables, rusty nails, precarious ceiling joists, bird poo, bat poo, rodent poo, mould spores, wasp nests, cluster flies, toxic dust and if you are really lucky a maggot-infested squirrel carcass.  To add to the discomfort the temperature inside a loft can reach 40 degrees Celsius or more on a warm summer’s day, which definitely provides an impetus to the inspection.

To be fair most lofts are fairly easy to access and the roof space often provides important clues as to the history and condition of the property. Old roofs are rarely perfectly flat and the reason becomes clear when you look at the underside of the structure. There are countless variations in traditional roofs, but in general, they consist of a series of trusses, purlins and rafters.

 

Late 18c attic room - Nicholson Price Associates

LATE EIGHTEENTH CENTURY ATTIC ROOM

A basic knowledge of historic roof construction will tell you the type of construction, a good knowledge will allow you to date the roof within fifty years or so, although this can be an imprecise method of dating the entire building.

Sagging ridge beams and purlins both contribute to the undulations that we commonly see in old roofs. This type of distortion gives the roof a more organic appearance and providing it is stable and the roof remains watertight, it is rare that anything needs to be done. The difficult part is deciding whether the structure has reached a point of equilibrium, or whether a good gust of wind and a couple of inches of snow might be the straw the breaks the camel’s back.

Making this type of assessment does not normally require the input from a structural engineer. All of the evidence is there, some of it physical, some of it documentary. If we tried to impose modern standards on historic roofs, in all probability many would not meet those standards. Three centuries ago there were no published span tables, structural calculations or computer models, the selection of timber and construction methods were based on observation and experience. Today we call this empirical design, 300 hundred years ago builders just used tried and tested methods.

Occasionally there will be a structural defect in the roof structure, the type of defect is very often age specific. By the eighteenth century, there was a clear change in roof construction, both in materials and methods. The change towards the use of softwood rather than hardwood and the rise of speculative housebuilding introduced a variety of problems that are not normally seen in earlier roofs. When I see the exterior of a building for the first time, I fairly quickly form a mental image of the roof structures. The position of windows and roof lights helps to establish where the floors and ceilings are located and whether the roof spread that is apparent externally is partly due to the feet of the rafters being untied.

The past and current use of the building can influence the condition of the roof structure. Changing economic and social conditions had a significant impact on many buildings and previously unused roof spaces were altered to accommodate family, staff or workers. It is common to find that the attic in a C17 building was clearly never originally intended for

Late 19c Cast Iron Chimney Flue Doors - Nicholson Price Associates

LARGE LATE NINETEENTH CENTURY HOUSE, CAST IRON ACCESS DOORS FOR CLEANING CHIMNEY FLUES

occupation and that the attic rooms are a later alteration. Evidence of an alteration includes the size and type of floorboards, introduction of roof lights, and the style of staircase and doors. Some of these later alterations resulted in the mutilation of the roof timbers which occasionally causes a serious structural problem.

Apart from structural problems, we are assessing the underside of the roof covering to help determine the age of the covering and also to assess the condition of the fixings. The production and history of nails are well documented and this helps us to decide how long the roof has been in place. The condition of the oak pegs traditionally used for fixing stone slates also provides us with a good indication of the likely life expectancy of the roof covering.

Condensation is becoming more prevalent in old roofs due to the introduction of insulation and the obsession with sealing every nook and cranny. The effects of condensation are usually clear to see, but where the underside of an old roof forms part of the ceiling, the damaging effects of condensation can appear elsewhere in the building. During a recent inspection, one of the ground floor ceilings had partially collapsed. After a bit of detective work, we found that the roof had been replaced with a non-breathable felt, as a result, condensation had formed on the underside of the felt, run down to the wall plate and saturated the wall below to such an extent that the ground floor ceiling joists had decayed. Anyone thinking that roof space ventilation isn’t that critical, think again, it can cause serious damage in old buildings.

Early 19th century attic room - Nicholson Price Associates

SIXTEENTH CENTURY ATTIC ROOM

Bats, as cute as they are can create difficulties for the owners or developers of historic buildings. In short, you can not disturb roosting bats. In practical terms, this means that if you want to undertake any work anywhere near a bat roost you will have to jump through a number of hoops. Nobody likes picking up poo but one of the simplest ways to distinguish between bat and rodent droppings is to rub the droppings between your fingers. Fresh mouse poo tends to be quite sticky whereas bat poo tends to be dry and often contains visible insect parts. This isn’t a foolproof test in my view and there are better indicators that bats are present, including the location of the droppings, the type of roof and obviously any anecdotal evidence provided by the owner or custodian.

It is not that uncommon to find large water tanks in a roof space. Some of the older ones are actually part of a rainwater harvesting system and when full can contain 500 litres or more. These are normally well supported but always require a close inspection. Another quite common feature in C19 buildings is the use of secret gutters which discharge into cast iron pipes that run horizontally through the floor or sometimes the roof space. This type of arrangement makes the inspection more interesting but the risks associated with a leak are easy to appreciate.

In most cases attic rooms have timber floorboards, these tend to vary in width from six inches or so up to almost two feet. Timber varies but typically this is oak, elm or a slow grown softwood. Very occasionally we come across something quite different. During a recent inspection of a C16 building, we recorded an earthen floor. This essentially looks like wattle and daub but it was laid over oak staves let into the floor joists. The finished surface resembled worn leather. Various materials were used in the construction and historical records indicate that blood was commonly added to produce a smooth surface. Although we avoided walking on this part of the attic floor, it was fully structural, although clearly highly susceptible to any sort of water damage.

After structural problems and damp, most clients are concerned with wood-boring insects. Without any hesitation, I can say that almost every roof we inspect has some evidence of wood-boring insects.

EARLY NINETEENTH CENTURY, EXCEPTIONALLY WIDE ATTIC ROOM FLOORBOARDS - Nicholson Price Associates

EARLY NINETEENTH CENTURY, EXCEPTIONALLY WIDE ATTIC ROOM FLOORBOARDS

There is an incredible amount of online information on this topic, some of it fact but a lot of it is opinion. It is a fact that roof timbers need to be fairly damp in order to sustain any meaningful infestation, the level at which the timber becomes too damp is more of an opinion. It is also a fact that insecticides will kill wood-boring insects, but whether and when they should be used again is a matter of opinion. I have seen very serious localised structural problems in major roof components caused by Death Watch Beetle, but in the same roof, more than 90% of the timbers were unaffected. This is always a difficult call. Best practice is always to remove the source of the moisture, but when there are no obvious sources of current water ingress and no realistic option for reducing ambient moisture, the choice boils down to a watching brief or some form of remedial action. Fortunately, most infestations within roof timbers have a clear cause, typically this is poor roof space ventilation, leaking gutters or defects in the roof coverings.

The contents of lofts and attics can either be a real hindrance to an inspection or provide a degree of interest and surprise. Evidence of the previous use of attic rooms includes utilitarian furniture designed for servants (even in modest sized properties), old candle sconces and gas light fittings. Former servant’s quarters also often retain historic paint schemes, usually some combination of chocolate brown, stone or green. Lofts which have only ever been used for storage usually contain a much wider variety of items belonging to previous owners or long-dead workmen.

FIFTEENTH CENTURY ROOF SPACE WITH LATER ALTERATIONS - Nicholson Price Associates

FIFTEENTH CENTURY ROOF SPACE WITH LATER ALTERATIONS

The extent of a roof space inspection depends on the geometry of the roof and the risks to people and property. There are a number of reasons why the entire space can’t be inspected these include; parts of the roof are completely sealed off, ceiling joists are unsafe to walk on, a bat roost would be disturbed, belligerent wasps are present. If it’s not physically possible to enter part of a roof safely then a strong light and a zoom lens is used to capture images of other areas.

If you are thinking of buying an historic building always make sure the surveyor checks the inside as well as the outside of the roof.

AUTHOR

Tim Nicholson, Managing Consultant of Nicholson Price Associates