Damp and Thatch

[Welsh Builder]

A big problem if the house uses lime mortar as well then?[/quote]

No, the opposite is true. Correctly applied lime render will soak water up from the ground (no DPC 150mm up, render run right to the ground) and allow it to evaporate away from the wall surface rather than percolate into the structure. Lime render is an essential part of keeping a thatched house dry. I would expect a thatched house with cement render to suffer badly from damp.

It isn't always about evolution. There were many tricks known to our forefathers which have been forgotten in the haste to adopt the most recently invented materials and methods.

 

[Nemesis]

Not all thatch is deep, not all walls render of course.

http://www.geograph.org.uk/photo/458464

 

[Stephen]

Thatch does not necessarily have a deep overhang by 'design'. Some thatch (particularly water reed) is a one coat mterial and is relatively thin with a mean overhang. However, much of the thatch tradition involves leaving a sound base coat and spar coating a new layer over it - hence an increasing eaves depth.

Some thatch does have guttering (very rae), but it has to be very wide to allow for the fact that the thatch gradually degades and wears away from the outer edge in- therefore the eaves is not a fixed line. A normal gutter would therefore have to be re-positioned evey few years. Therefore most thatch has no guttering and has a drip line that gradually moves closer to the house as the eaves degrades. Provided the ground under the drip line is soft (earth, grass or gravel) the water percolates into the soil and there is no problem. The modern tendency to have concrete 'aprons' to buildings means the water drips onto a hard surface and bounces into the walls.

With traditional finishes to the building blown rain off thatch is rarely a problem and splashing at the base is not usually a problem.

We now know that many historic buildings (certainly those pre C16) had deep overhangs and no gutters. Many home owners then could not afford the luxury of gutters therefore the roof eaves simply discharged water onto the ground. There are pros and cos with the issue of gutters v no gutters. No gutters disperses water over a wider area and fairly evenly around the building, but there is a risk of rain blown onto the wall or splashing into the base of the wall. Gutters bring an increase in maintenance and if they fail concentrate large volumes of water in one area. If there is no soakaway, etc the downpipe leads to large volumes of water discharging at the base of the wall in one specific area (often a cause of localised movement and dampness). However, if gutters, etc work properly they take the water well clear of the house.

I hope the above helps in your debate.

Stephen

 

[Flyfisher]

Interesting point about the drip line of thatched roofs changing over time as the thatch degrades. I can now see why guttering on such roofs is very rare.

While in Cornwall last month, I noticed (how sad is that?!) lots of guttering downpipes that discharged directly onto the ground, often pavements, with apparently no attempt to take the water away from the property. Given this, it hardly seems worth the additional maintenance of guttering in the first place, although I suppose it saves being dripped on whilst fumbling for the front door keys.

 

[Nemesis]

Causeway House (Landmark Trust c 1780) after a recent re-thatch with ling (heather) known here as 'black thack':

http://www.geograph.org.uk/photo/764891

Also, http://www.geograph.org.uk/photo/886453

I don't think this has any guttering. I will go and check.
It belongs to the Historic Chapels Trust.

The Exterior
A single storey stone rectangular building - 13.1 metres long by 6.2 metres wide - and the date 1760 is inscribed on the lintel above the door in the south side. The original 18th century roof was covered by heather-thatch. However, it was replaced early in the 19th century by one with a double course of flagstones above the eaves, Welsh slates, and a stone ridge. There are three original windows on the south side, all with 12 panes. Attached to the front of the east wall is an earth closet.

The Interior
The interior has a stone flagged floor and is divided into two by a panelled wooden screen. The larger room to the west is the main meeting room with a central aisle dividing seven rows of open-backed wooden benches facing west. At the west end, two additional rows face the other seven and are raised – sometimes called Elders’ benches.

My own house in the area c 1800 I don't think originally had guttering, that I suspect would have had a stone roof at the time of building. I also think the drainage from the roof is late 19th century. One roof drained straight into a pipe fed into the septic tank, I suspect before that was installed it fed into a barrel to aid water supply, which until around 1950 was got from a well about 50 yards away, or the adjacent burn.

I know many houses where the guttering discharges onto the pavement, to then run into the general road drains. Large numbers of these would have been built before drainage was installed into made-up roads.

http://isee.gateshead.gov.uk/detail.php?t=objects&type=all&f=&s=terrace&record=15

 

[MdB]

While in Cornwall last month, I noticed (how sad is that?!) lots of guttering downpipes that discharged directly onto the ground...

I didn't realise this was a Cornish thing. I just thought it was our house .

 

[Ushy M]

Thatch owner out here! Late response as no chance to catch up on PPUK all week. In our case, at the front of the house, rain falls from the thatch onto the pavement (very quickly - the steep pitch of thatched roofs is intended to shed water briskly so it doesn't hang about and soak in) and yes, the ground does stay wet for a bit till it flows onto a bit of grass beyond.

Rain at the back falls from the thatch onto the (tiled) extension, into the extension gutter then into 'well' or cistern near back door. No problems with damp (especially as we gradually replace the cement pointing with lime), except when trying to get into the front door in the pouring rain (no porch) when all the water runs down your back . On the plus side, no gutters on the main part of the house means we get a £30 rebate from Anglian Water .

 

[Penners]

no gutters on the main part of the house means we get a £30 rebate from Anglian Water

I never knew that. Presumably this is because your surface water doesn't discharge into the sewage main?

That being the case, could I get a rebate for the areas of my roof whose guttering downpipe discharges into a soakaway in the garden?

What exactly are the criteria?

 

[Flyfisher]

You may not be eligible if some of your roof discharges into mains drainage. This might be interesting: http://members.aol.com/wwanglia/31.htm or Google 'anglian water drainage rebate' for loads more info.

 

[DaveBrigg]

I looked at the rebate recently, after having dug french drains and soakaways at various points around the house. Two things cropped up - one, that the rebate will only be applied at the start of a financial year (apparently they allocate all their funds then, and would not be able to cope if you wanted £30 back in July). Secondly, it can only be claimed if surface run-off from a driveway does not enter an Anglian water sewer. Our driveway is fairly level and consists of a patch of crumbling tarmac. In a heavy downpour however, some of the water probably goes into the road. Do I need to dig a moat across the driveway to divert any runoff into the garden?

 

[Ushy M]

We had to apply in writing on a form from the water company, which includes some questions about soakaways and whether water drains onto the surface of yours or someone else's property and whether this goes into Anglian Water's drainage. We also had to draw a simple map of the property including outbuildings, indicating rainwater flows from the various roofs.

However, the water company is unlikely to come and check - particularly if they know it's a thatch (no gutters!). Even if some water drains to a water co. drain, there should still be a portion of the rebate for parts that don't. The rebate amount may be different of course for different water cos.

 

[Penners]

This might be interesting: http://members.aol.com/wwanglia/31.htm or Google 'anglian water drainage rebate' for loads more info.

Thanks FF, Dave and Ushy.

Based on your explanations, I don't think I would qualify. However, I strongly suspect that my daughter's thatched property would. I'll encourage her to check.

 

[Nemesis]

We only pay for water, not water and drainage. Septic tank and water runoff into the adjacent burn.