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Damp prevention from adjacent propert? (Read 1107 times)
moffer
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Damp prevention from adjacent propert?
Jan 18th, 2021, 8:25am
 
Hi, my nextdoor has just forwarded plans for a two story extension next to mine. We live on a hill (he is uphill of me) which means the base of the new extension will be approx 18" - 24" above mine. There will be a narrow gap between the adjacent extension walls, I'm not sure how wide, but would think around 6" or so. What concerns me is preventing rainwater entering the gap at the top of the  extensions and causing damp issues on my ground floor. Obviously there will be normal roof gutters in place but I'm not entirely happy with just that due to possible overflow, and wonder what else can be put in place to prevent rain water entry such as a way to seal off the top of the gap? I'm also concerned about additional possible damp issues from cement slops (think that's the term) dropping down and building up at the bottom of the gap when the block wall is being built and how to prevent  this happening?

I have looked at the plans but, surprisingly perhaps, there is nothing on there about rainwater drainage between the two extensions. I get on well with my neighbour and will be dicussing my concerns with him, but would like to have some idea what I'm talking about so will appreciate if anyone can help?

Hope the above is clear?

With thanks
moffer
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woodsmith
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Re: Damp prevention from adjacent propert?
Reply #1 - Jan 19th, 2021, 8:01am
 
If your extension has a cavity wall then, as long as they don’t bridge your damp proof course, rainfall in the gap between the two houses shouldn’t cause a problem. It’s bridging the damp proof course, by building the ground up too much, which causes most problems. If they have a good builder they should ensure there are no problems. If you are still worried you could ask at the building control department of your local council as they will need building control approval before starting any work.
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moffer
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Re: Damp prevention from adjacent propert?
Reply #2 - Jan 19th, 2021, 4:54pm
 
Thanks for that woodsmith, the problem I have with just conventional roof guttering on both extensions is...firstly from overflow due to heavy rainfall and when the time comes, as it surly must, how do I repair or renew my gutter when it's so close to the wall of the new extension, which is approx 2 foot higer than mine due to living on a fairly steep gradient and my house being downhill. I don't know much about building hence why I've aked here, but I would think that along with guttering, the top of the said gap needs some sort of secondary sealing such lead flashing. There are no details on the plans regarding the width of the gap or or proposed method of rainwater drainage, not even guttering, which surly there should be!? Makes you wonder how the council approved them! I plan on having a chat with my neighbour tomorrow to get some clarity.  I'll  probably do as you advise and get in touch with the council as well.

If you think I'm being overcautious or even paranoid, I can assure you that I have good reason as I've had serious damp issues along my extension wall before related to irresponsible rainwater drainage by this neighbour.

edit...if the gap is narrow as it appears to be looking at the plans, then there must be a concen for cement droppings building up above my extensions damp course when the two storey wall is being built. That is why I asked innmy initial post what a brickie would do to prevent this. Once this extension is up, it's up, and it will be too late or costly to sort any potential damp issues so I need to get it right.
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Re: Damp prevention from adjacent propert?
Reply #3 - Jan 20th, 2021, 9:15am
 
Are you saying that your roof comes down toward your neighbour and there is guttering along this edge which will more or less fill the gap between the two houses? If so that doesn’t seem right and you should definitely go to Building Control and get them to look at this. I assume your neighbour didn’t need planning approval for this otherwise this could have been sorted at an earlier stage.

As for mortar getting into the cavity, good brickies are used to keeping the cavity clean to prevent damp bridging.

You may be able to dig the ground down between the two houses prior to building to help to keep damp away from your wall or replace any soil with 10mm gravel which will aid drainage.

You can’t be too careful with damp problems, and it’s definitely worth it, for both you and your neighbour, to get this sorted before any building work starts.
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Natedog
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Re: Damp prevention from adjacent propert?
Reply #4 - Jan 20th, 2021, 5:15pm
 
our extension was built with a very small gap between it and next door's extension.  both roofs slope towards this gap and rainwater feeds into a single gutter.  i'm not sure which house the gutter is fastened to.  

it does cause problems!  moss from the roof and other stuff gets washed into the gutter and cleaning it out isn't particularly easy.  at some point in the past, someone has tried poking something along it and knocked the end cap off.  there is no way of replacing this so if there is lots of moss and some heavy rain it overflows down the back wall of the original house.  this does let some damp appear in the upstairs rooms as the original house is just a 9" thick solid brick wall.  

The only feasible solution i can see to our roof would be to put a proper valley in.  but we have the advantage of both roofs being the same height.  

would you be able to get a valley fitted?

when my mum had her extension built back in the mid 90s, building control insisted on a gap between her extension and next door that was big enough for a person to get in to allow for any maintenance required.  whilst this does make for a smaller extension, it is definitely the route i would choose.
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Re: Damp prevention from adjacent propert?
Reply #5 - Jan 21st, 2021, 2:30pm
 
woodsmith wrote on Jan 20th, 2021, 9:15am:
Are you saying that your roof comes down toward your neighbour and there is guttering along this edge which will more or less fill the gap between the two houses? If so that doesn’t seem right and you should definitely go to Building Control and get them to look at this. I assume your neighbour didn’t need planning approval for this otherwise this could have been sorted at an earlier stage.

As for mortar getting into the cavity, good brickies are used to keeping the cavity clean to prevent damp bridging.

You may be able to dig the ground down between the two houses prior to building to help to keep damp away from your wall or replace any soil with 10mm gravel which will aid drainage.

You can’t be too careful with damp problems, and it’s definitely worth it, for both you and your neighbour, to get this sorted before any building work starts.


Yep, that is more or less what I'm saying. I'll try to clarify further....I live in a terraced house on a steepish hill. Nextdoor's house is uphill of me, hence his house and backyard are approx 18 - 24" higher than mine, as will the proposed 2 storey xtension. His new xtension roof will be higher than mine, which means a conventional gutter on my xtension roof will more or less butt up against his new xtension wall. Along with gutters getting blocked and possibie overflow during heavy rain, which is happening more frequently these days, I won't be able to renew the gutter when needed as there will be no room to work.

I'm no buider obviously, but I'm thinking of some sort of flashing or whatever to cover the top of the gap. As double insurance, I'm thinking of clearing a couple of inches of dirt along the bottom of the gap, as you mentioned,  and channeling any water that gets in along a plastic or earthenware gutter into a nearby drain in my backyard. I'm thinking of bedding the gutter into a layer of cement, which will cover the whole of the bottom of the gap. Making sure to stay below the dampcourse of my xtension, which has a cavity wall by the way. I'm willing to pay for that secondary preventative providing  the top of the gap is sorted to my satisfaction. Remembering that my neighbours backyard is also 18" - 24" higher than the floor of my xtension, but there is a 9" gap between their backyard along the entire length of my xtension. My builder made sure of this when he built my xtension many years ago. He prevented rainwater entering by capping off the top of the gap with a single course of house bricks and capping stones cut to suit to prevent rain water entering. A good job he made of it too until my neighbour kindly decided to remove the end capping stone and insert a downpipe from his main roof down into the gap, which caused me a whole lot of damp problems before I eventually found outwhat he'd done!

As you can see it's all a bit complicated and not easy to explain but I hope you get the picture? Wouldn't mind knowing if you think of my two methods of rainwater prevention are feasable?? I'm old enough (70 years) to have learned not to leave anything to chance, so as you suggested I have been in touch with building control both by email and later by phone. I have to phone back next week. Not seen my neighbour yet but will have a chat when I bump into him.

How on earth does the local authority allow plans through when they are clearly not detailed enough? Compared to the plans drawn up for my xtension, my neighbours look as if they are meant for a dolls house.

Thanks for your advice and time, tis much appreciated.

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Re: Damp prevention from adjacent propert?
Reply #6 - Jan 21st, 2021, 3:26pm
 
Natedog wrote on Jan 20th, 2021, 5:15pm:
our extension was built with a very small gap between it and next door's extension.  both roofs slope towards this gap and rainwater feeds into a single gutter.  i'm not sure which house the gutter is fastened to.  

it does cause problems!  moss from the roof and other stuff gets washed into the gutter and cleaning it out isn't particularly easy.  at some point in the past, someone has tried poking something along it and knocked the end cap off.  there is no way of replacing this so if there is lots of moss and some heavy rain it overflows down the back wall of the original house.  this does let some damp appear in the upstairs rooms as the original house is just a 9" thick solid brick wall.  

The only feasible solution i can see to our roof would be to put a proper valley in.  but we have the advantage of both roofs being the same height.  

would you be able to get a valley fitted?

when my mum had her extension built back in the mid 90s, building control insisted on a gap between her extension and next door that was big enough for a person to get in to allow for any maintenance required.  whilst this does make for a smaller extension, it is definitely the route i would choose.  


Thanks for that Natedog, at least my fears are not unfounded after reading your post, and like you say, next door is higher than me so that creates more difficulty.

No way am I going to accept a conventional gutter for the reasons I've given. Some sort of valley is what I'm thinking too, but that won't be easy due to the height difference but next door's architect & builder will have to sort that out! There are no details on the drawing regarding rainwater drainage or the width of the gap, which has made me more than a little suspicious what they have planned. This is the second set of plans as the first were opposed by next door up the hill from my neighbour due to loss of light. That was the normal way of doing xtensions in my street and would have left several feet between my xtension and the one proposed. Next door up from my neighbour will still be losing light, but not as much with the new design so they might object again,which would save me a lot of hassle if they do.

I've got very nice views of the surrounding countryside by living on a hillside, but it does come with baggage.


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Re: Damp prevention from adjacent propert?
Reply #7 - Jan 21st, 2021, 7:01pm
 
The issues is mentioned here..

https://www.blsurveyors.com/weatherproofing-a-gap-between-two-properties/

The problem is that connecting the two properties together with some sort of flashing makes them into a semi rather than a detached so loosing value.

First thing I would check is the boundary line. This can be hard to determine but in general nothing (including gutters) should overhang the boundary. If your gutter will be close to the wall of their extension will their gutter/verge end up overhanging your gutter and hence overhang the boundary?  If so get this sorted before they start building any of the wall. Once they start they will be too committed to fix it by moving the wall.

Is your fascia wood? Perhaps ask of you can replace it with plastic before they start?








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Re: Damp prevention from adjacent propert?
Reply #8 - Jan 21st, 2021, 7:18pm
 
Have they applied for planning permission? If so I would object in writing on the grounds that it will make maintenance of your wall impossible and cause drainage and damp issues due to the accumulation of leaf debris.

Add you would have no objection to their extension if the gap was increased to ?? some value.

Beware you only have a limited time period to object and they will only consider "valid planning reasons". Loss of property value or a view is not considered a valid reason.

moffer wrote on Jan 21st, 2021, 3:26pm:
No way am I going to accept a conventional gutter for the reasons I've given. Some sort of valley is what I'm thinking too, but that won't be easy due to the height difference but next door's architect & builder will have to sort that out!


They are higher than you so its unlikely they will need to dig deeper than your foundations so I don't think they need to comply with the Party Wall Act. Unfortunately this means that once granted planning permission there is little or nothing you can do to stop them building right up to the boundary. The situation would be different if they were having to use piled foundations.
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Re: Damp prevention from adjacent propert?
Reply #9 - Jan 21st, 2021, 10:27pm
 
CWatters wrote on Jan 21st, 2021, 7:18pm:
Have they applied for planning permission? If so I would object in writing on the grounds that it will make maintenance of your wall impossible and cause drainage and damp issues due to the accumulation of leaf debris.

Add you would have no objection to their extension if the gap was increased to ?? some value.

Beware you only have a limited time period to object and they will only consider "valid planning reasons". Loss of property value or a view is not considered a valid reason.

moffer wrote on Jan 21st, 2021, 3:26pm:
No way am I going to accept a conventional gutter for the reasons I've given. Some sort of valley is what I'm thinking too, but that won't be easy due to the height difference but next door's architect & builder will have to sort that out!


They are higher than you so its unlikely they will need to dig deeper than your foundations so I don't think they need to comply with the Party Wall Act. Unfortunately this means that once granted planning permission there is little or nothing you can do to stop them building right up to the boundary. The situation would be different if they were having to use piled foundations.


Thanks CWatters, that complicates things a little.  We live in a terraced block so making my house into a semi doesn't really come into it I would have thought. Along with a phonecall to the council building control, I 've also wrote them a letter within the objection time period of 28 days expressing my concerns and explaining the above issues. I get on well with my neighbour and will be discussing the matter when I see him, which isn't easy as he works weird shifts. Hopefully we can come to an agreement, but I'm going by the book by informing the council about the issues so I know where I stand just in case I can't come to a satisfactory arrangement with my neighbour. As mentioned, I'm quite willing to pay for any additional work such as the said drainage gutter at the bottom of my extension. I've been told by the council officer who deals with  objections to phone him back next week when he has looked into it further and will have more information for me. I know little about planning regulations, but how someone can erect a bulding that can cause problems with a neighbours property doesn't figure with me, but it wouldn't surprise me if such things are allowed. Anyway, hopefully I'll  find something out when I phone the council back on monday.  
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Re: Damp prevention from adjacent propert?
Reply #10 - Jan 22nd, 2021, 9:58am
 

I don’t think that the damp at the bottom of the wall should be a problem as long as ground levels are not raised. Adding extra drainage in the form of 10mm gravel would be a good idea (you could even add a land drain as they are relatively cheap and easy to fit if you wanted to be extra careful). So I don’t think this is something you should object to with regard to planning, it’s the roof and gutter, and the inability to maintain it in the future, that is the problem and this is what you should concentrate on when contacting the Planners.

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Re: Damp prevention from adjacent propert?
Reply #11 - Jan 22nd, 2021, 11:30am
 
woodsmith wrote on Jan 22nd, 2021, 9:58am:
I don’t think that the damp at the bottom of the wall should be a problem as long as ground levels are not raised. Adding extra drainage in the form of 10mm gravel would be a good idea (you could even add a land drain as they are relatively cheap and easy to fit if you wanted to be extra careful). So I don’t think this is something you should object to with regard to planning, it’s the roof and gutter, and the inability to maintain it in the future, that is the problem and this is what you should concentrate on when contacting the Planners.


I appreciate that the roof and gutter are the main issue and that is what I'll be concentrating on with the council. Any drainage system at the bottom of my extension would be a secondary prevention, which I'm willing to pay for, may not be needed if I'm satisfied with whatever method of controlling rainwater they decide to use at roof level. Even if I'm happy with that it wouldn't hurt any to do a bit of digging and line the bottom with gravel as you suggested.

I'll update after the council get back to me.

Thanks again.
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Re: Damp prevention from adjacent propert?
Reply #12 - Jan 28th, 2021, 10:59am
 
Just to let you know that I've spoke with my neighbour about the lack of detail on the plans. He told me that they are not complete and phoned his architect to find out what the plans were regarding my extension. Apparently the architect has done a number of similar extensions and said there wll be a narrow gap between both extension walls, my neighbours walls are going to be woodframe and not cavity block. It will be properly sealed at the top and will be repairable if it ever leaks. I told my neigbour that I also want 9" of dirt dug out from below my dampcourse and filled with chippings, which I'm willing to pay for. My only concerns now is it seems as if there will be 2 downpipes going into a single drain in my backyard. One will be for rainfall on one side of my extension and half of my main roof. The other downpipe will have to control the same amount of rainfall from my neighbours house. Perhaps I'm being overly concerned here, but that does seem a lot of water going into one drain to me! Maybe one of those bucket things, think they're called cherry boxes,  at the top of my  downpipe will help there? Any thoughts on that will be welcome?

Not happy with the slow response from council building control who were dragging their feet. Even more unhappy that I was given notice that I had 28 days to object to plans that hadn't been completed! Just what is that supposed to be about?!! With less than a week left to object and not even verbal reassurance never mind written, I had no choice but to write a letter of objection forwarded to the council last tuesday. I explained the situation to my neighbour when I spoke with him who understood my position.

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Re: Damp prevention from adjacent propert?
Reply #13 - Jan 28th, 2021, 5:55pm
 
How the hell are they going to service or even clad a timber-framed building with a 6" gap?..

Also, their drainpipe should go into a soakaway in the neighbours garden on drain if it's allowed
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Re: Damp prevention from adjacent propert?
Reply #14 - Jan 29th, 2021, 8:47am
 
This sounds very rum to me. How can they ask for planning with incomplete plans? And I agree with Scruff, having a timber framed wall that is completely inaccessible is madness. Plus the architect needs to explain how it’s going to be repairable of it ever leaks.

As for the drain, your neighbour needs his own soak away if you are not on mains drainage.

In my experience Councils do nothing until the very last second. Hopefully they will ultimately refuse this and demand better plans.
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