Timber rafters and beam

[Julesr6]

Hi,
I live in a former chapel, in wales, built in 1808.
The timbers are showing signs of rot, some of the rafters have had repair work, approx 20 years ago, the repairs are between the ridge and the first purlin, the second purlin is exposed under the ceiling.
Does the ridge beam look ok? Would it be ok to repair some more rafters between the ridge and the first purlin.

Thank you

 

[jamest]

In my experience, 200-400 year old rafters and ridge beams can look pretty grotty and yet be perfectly serviceable. Some of mine look as grotty or grottier than yours and they're fine. A bit of historical surface rot and worm damage in old oak rafters is usually confined to areas of sap wood. As long as everything is dry (and it looks pretty dry in the photos), it's likely got plenty of life left in it.

What one can't see in your photos is whether there is any sign of sag in the ridge beam or the rafters and corresponding sag in the roof viewed externally. If there is no sag, then it's probably fine given that there are no splits across the grain (no sign of that in the photos). Individual old rafters can sag quite badly before they split cross-ways and fail. They do tend to be less deep than modern rafters (which are narrower but much deeper) and with age they can fail, but a bit of sag is usually not a problem.

If there is evidence of cross-grain splits or significant sag, you could sister up the suspect rafters between the ridge and purlin. Might be a good idea to get a professional opinion though.

 

[Cubist]

From a few photographs it's impossible to tell and to offer any kind of judgement. I would want to get up close and personal with a mallet in my hand. Appearances can be deceptive and the feel of the wood and the sound it makes when rapped can be much more revealing than visual inspection alone. My best advice here would be for you to seek the opinion of a either a roofer with credible experience of working with old timber structure roofs or a timber framer with experience of old buildings and check their references before you let them near the job.

 

[Julesr6]

Thank you very much for your replies.
Attaching a couple of external pictures.

Thank you

 

[Julesr6]

Bit of sagging on the ridge but I think the rafters look ok?

 

[jamest]

Looks to be some minor sag in the ridge, but very little dishing in the roof covering. Better than mine, which causes me no worries at all.

If there are no actual problems, then there's nothing to fix! However, if you are worried about the condition of the beams and rafters, check thoroughly for cross-grain cracks and as Cubist suggests give them some taps with a mallet (or something), a poke suspect areas with a screwdriver and check for any dampness or evidence of water ingress. If they sound solid, are dry and the screwdriver does not penetrate more than a few millimetres before hitting hard wood, then probably no worries. However, if you do find something, get a professional to take a look and advise - you really can't tell much from pictures. Someone needs to give it an a thorough inspection and advise if you locate anything dodgy.

 

[Cubist]

A few things about this roof have been nagging me;

1. The material behind the rafters and ridge pole appears to be roofing felt. This did not come into common usage in the UK until the 1950s and before that a paper system would have been used from the 1930s. This is making me think that at some time this roof was completely stripped back to the frame.
2. Many of the timbers look to have suffered water damage to produce the black staining many exhibit. This could have occurred during the buildings original construction or when the roof was stripped later.
3. Assuming that the pegs used in the main trusses are the typical 1 inch and using this as a guide, the dimensions of the ridge pole(s) can be estimated at roughly 4x4inches and its likely that at least two poles would have been used in the roofs construction.
4. The timbers used to either replace or repair failed rafters or to add support to a weakened rafter using the sistering technique appear to be pressure treated pine and can have no direct connection to the ridge pole unless this new timber was installed while the roof was stripped.
   1. With no direct connection to the ridge pole this later additions function is limited to perhaps preventing dishing alone. But, the additional weight transmitted to the ridge pole may still contribute to sag.
   2. Pressure treatment for timber was introduced in the 19C but these timbers appear much newer.

In addition the latest photo shows that three modern vellum windows have been installed at some point. This prompts questions regarding whether any rafters were cut to allow installation and how exactly any additional supporting woodwork was installed.

 

[Julesr6]

Thank you Cubist and Jamest.
I have given a few rafters and a ridge beam a poke with a screwdriver, generally quite solid, a few could probably do with a sister. The ridge beam is 5”by 5”, the purlins are 7”by 7”. The sister rafters only go from the ridge to the upper purlin, so may be able to add more internally without removing roof?the velux sit on the lower purlin.

Thank you

 

[Julesr6]

Roof was stripped back and felt added approx 20 years ago.

 

[Cubist]

The sister rafters only go from the ridge to the upper purlin, so may be able to add more internally without removing roof?

Thanks for the additional data/confirmations. Yes you should be able to do that but don't be tempted to drive any long screws through the ridge pole - that's the only way they could have been permanently fixed with the roof in place.

BTS - is that copper pipe still in use for the gas or water service? If so, best replace it sooner rather than later.

 

[Julesr6]

Thank you Cubist.
I think the copper pipe is now redundant, the old header tank is underneath it.
Why would it need replacing if still I use?

Thank you

 

[Cubist]

If it were a water pipe that level of corrosion could lead to pin-hole leaks or a complete burst, both of which are bad news in a loft space. On the other hand a gas leak could make things go bang in a very unpleasant way.