All buildings need maintenance from time to time. For various reasons and neglect of maintenance is one, repair is also needed. Historically significant buildings are often conserved; that is they are maintained and repaired in ways that maintain the special historic interest and character of the building.
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Simple measures can be taken by the property owner to ensure the thatch has the best chance of performing well.
- Removing branches of trees that over hang the thatch. These can restrict solar heat and wind turbulence, keeping the thatch damp. Drips can also cause mechanical damage.
- Remove leaves that become lodged in wire netting and that stop the thatch from drying out.
- Fix television aerials or dishes inside the roof space where possible. If this is not possible try to fit them away from the thatch and not on chimneys, as this will eliminate the need for technicians to physically get on to the thatch in order to carry out any repairs or renewal of such equipment.
As a general rule, the less disturbance of thatch the better, so it is important that no one gets onto the thatch unless absolutely necessary.
Moss, Algae and Lichen
Moss and algae can indicate that the surface of the thatch is consistently moist enough to support growth. However, its presence usually indicates a damp environment rather than a failing thatch. It isn’t necessary to remove moss and the effects of moss killer treatment and algicides on the thatch itself is little understood and should be avoided.
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Repair & Conservation
Many thatched property owners like to have their property looking ’just thatched’. Although this looks pleasing, it is not an indication of healthy thatch and unnecessary re-thatching is a needless expense. As an organic and biodegradable material, thatch will start to decay as soon as it is put on the roof. The warm, golden colour that is so pleasing will soon darken and go grey. But even as it changes visually, a thatched roof will have many healthy years.Stripping and Re-thatching
Re-thatching of water reed usually involves stripping the old water reed roof back to the timbers. It is generally fixed with iron crooks directly to the rafters and so this requires all existing thatch to be removed and the rafters to be sufficiently structurally sound to withstand new fixings. Consequently, ancient thatch is removed and disguarded and historic rafters are replaced. This seems more to do with convention than necessity, although in some regions where the roofs are more steeply pitched it has been found that reed can not be attached securely to existing thatch coats. Some thatchers prefer to re-thatch in water reed for reasons quite unrelated to conservation issues. Tying (which takes longer) and/or screw fixings can be used to attach reed to rafters.
This may be termed ’restoration’, that is to return a place to a known earlier state, on the basis of compelling evidence, without conjecture. However, understanding the materials of the earlier state is sometimes contentious.
There are few individuals with the knowledge, skills and experience to undertake an archaeological investigation.
Here are some of the repairs that may be necessary from time to time.Re-ridge
The ridge is an essential element and will need replacing several times during the life of the main coat (approximately every 7-10 years). It should be replaced before it has deteriorated to the stage where water ingress may damage the main thatch.
A ridge can be thought to be in need of replacement when:
- The ridging material has eroded or slipped leaving the spar fixings protruding by 2 inches or more.
- When the ridge has depressed, or the basecoat is showing through.
Decayed thatch can be removed, and the area is made level with the surface of the adjacent thatch, using rolls or wads of straw tied with string or straw bonds, secured by sparring into the thatch below. It is then re-thatched in overlapping courses and secured with surface sways and liggers. At every course the patch is widened to ensure the one below it is watertight, and the final upper course is tucked under an intact course, or (if the patch reaches the top of the roof) under the ridge. If decay extends through the full thickness of the thatch, all the area must be stripped back to the timbers and new bundles tied to the rafters to form a base coat, before repairing as described above. Care should be taken to avoid disturbing the main coat of thatch on either side of the patch.
Traditionally, smaller areas requiring repair were patch repaired. On a long straw roof this new material is referred to as a ‘stob’. However, this type of repair can only be used where thatch has been fixed with tied sways. If spars have been used they restrict the ‘stob’ being fixed into place.
Eventually the thatch will deteriorate to an extent that the majority of its surface area no longer sheds water effectively. At this stage, it will be necessary to apply a new coat. This is called re-coating, spar coating, or overlaying.
There is clear evidence that this method was used historically, and over the course of a thatched roof life these layers could accumulate, increasing the thickness of the thatch. However, few historic roofs are more than 1.5m thick and so it would seem that once the thatch became greater than 1m thick, the previous spar coat was removed entirely before attaching a new one.
If the existing thatch is left, new thatch work is applied between 250 – 300mm thick, which can increase the overall thickness. Building up the thickness too much can be detrimental since it not only adds weight to the roof structure, but reduces the height of chimney stacks which can potentially increase the fire risk (read more in Fire).
Any base coat being over-thatched must be tight and well-secured to the roof frame. Any sodden or decayed material should be carefully removed and replaced and any loose material re-fixed. This will then provide a sound surface into which the fixings of the subsequent new thatch can be anchored.
If the basecoats are no longer secured to the roof frame, measures will need to be taken to ensure that further slippage is avoided by reattaching the basecoat to the timbers. This will need to be done sensitively to avoid further damage to the underlying structure. This option allows as much of the historic thatch to be retained and keeps the new material (and costs) to a minimum.
Any structural faults affecting the primary roof structure must be addressed, following advice from a suitably experienced building professional, prior to repairing the thatch itself. Some thatchers undertake this carpentry work.
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