Full plans response - drainage and ventilation issue

The LABC have responded to my front extension plans, and I'm reasonably pleased that they've only picked up on three areas Thanks to everyone that's helped get me this far over the past few months!

1) I'd not made clear that the lead flashing up-stands were 150mm. In the scale drawing they were actually more like 90mm, so I've corrected this, and this will push the roof angle down to around 28 degrees. I'll be using rosemary tiles, so is there some kind of low-pitch roofing felt I should specify at this stage?

2) Means of ventilation: "please provide details of ventilation to room enveloped by extension" Presumably they're referring to the lounge, which will have its existing external window turned into an internal wall/window. As a whole the house has around three trickle vents on windows, and no air bricks. The lounge has a chimney with gas fire feeding into a check plate, but you can tell the fire lets in a draft from its bottom. The opposite end of the room has sealed doors into a sealed conservatory. The the plan below, the new extension is the porch/lobby top right, and the lounge is the room top left:


So I'm not sure what they're looking for here. An air brick? Or will my chimney statements suffice?

3) Rainwater drainage. "Please provide full details of rainwater disposal from extension roof" The existing storm shelter roof that I'm replacing like-for-like has no guttering and runs onto the tarmac drive, and there's a gentle gradient away from the house into the lawn. I'd been a bit cheeky here and stated that I was going to fit guttering and join it into the main house roof down-pipe. Obviously this isn't sufficient detail. I have no idea where the main roof down-pipe goes - it's buried in a hedge and I suspect it just flows into the ground. I'll have a closer look later:


So - if I have to dig a soakaway, is there a dimensional lookup table that I can use to calculate the size required?

Thanks

Gary

Soakaway 1m x 1m x 1m with 100mm clean fill will be fine - only thing is, it has to be minimum 5m away from the building.

Ventilation is a problem. Rooms have to have a rapid ventilation opening at least 5% of the area of the enclosed room - and part of that has to be 1.7m above floor level. That is normally covered by the window which you will not now have. You do have a window/door at the other end though. Is the openable area of that 5% of floor area?

The french doors measure approx 1M wide by 2M high, both open fully. The lounge is around 3.5M x 4.5M = 15.75M2, so that'd be 12%. Would they class as ventilation, given that they are external doors opening into a conservatory?

Thanks

Gary

By clean fill - presumably you mean rubble? I'll be breaking up the existing concrete slab so that could work out nicely. The lawn is around 5M away from the house, so I suppose that's not too much of a problem, but I'll need to cut through the tarmac to lay a pipe, which is a shame.

Gary

garyo said:

Would they class as ventilation, given that they are external doors opening into a conservatory?

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I don't think that will be satisfactory as there needs to be natural ventilation from the outside so this door you're referring to would merely be deemed as internal, not external doors.

garyo said:

By clean fill - presumably you mean rubble?

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The soakaway should be filled with non-degradable non-compressible materials, usually single sized drainage stones or hardcore and it should be lined with a suitable geotextile material (e.g. Terram 500S).

garyo said:

I suspect it just flows into the ground. I'll have a closer look later:

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Then your new drainage can also drain onto the ground then unless it runs into a neighbours garden or down a path etc, the rain that falls where the extension is being built absorbs the rain at the moment so you're not making anything worse. Soakaways fine unless you're on clay.

Yes, I'm on clay. I've read in the archives that a number of people have been forced to install pointless soakaways in clay to please building control.

My first drainage submission was this one:



So I could change it so that it shows the lawn, flower beds, and hedge between us and the neighbour. Is it acceptable for the water to flow from the drain pipe, over the tarmac that cars are parked on, and into the lawn? i.e. what would be my chances with this :


Thanks

Gary

Phone up the inspector and ask him if he is prepared to accept you draining over the existing ground as that is where the existing is draining, it needn't spill all over the path, you can guide any rainwater with a fluted footway channel 2nd one across in this pic:



They're extremely common down this neck of the woods.

Admittedly you don't want to end up with a hole in the ground where the water pools though so not ideal.

Your inspector should know off the top of his head if a soakaway will work as he should be familiar with your particular area. You may have to do a soakaway percolation test to prove a soakaway won't work. If he won't accept it spilling onto the ground and a soakway won't work he should let you branch into the mains drainage.

edited for grummer!

Ventilation through a conservatory is fine but you have to add the floor areas of the room and the conservatory together and both sets of openings must be at least 5% of the total area.

garyo said:

1) I'd not made clear that the lead flashing up-stands were 150mm. In the scale drawing they were actually more like 90mm, so I've corrected this, and this will push the roof angle down to around 28 degrees. I'll be using rosemary tiles, so is there some kind of low-pitch roofing felt I should specify at this stage?

Click to expand...

Rosemary or plain tiles are only suitable on pitches 35 degrees or steeper.
Sounds like you need a concrete interlocking tile.

Rosemary or plain tiles are only suitable on pitches 35 degrees or steeper.
Sounds like you need a concrete interlocking tile.

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I'd really like to use the existing tiles as they match the house - can I fit a more expensive rubber/felt system underneath?

Thanks

Gary

I've just had a chat with a nice officer at the LABC.

Ventilation - as you guys have pointed out, I can use the combined area of the lounge and conservatory, and then calculate the area of the conservatory external doors and windows. These are something like 5.8% so I need to go measure accurately to make sure.

Drainage - I need to build an underground pipe from the new extension, to carry the water at a 1 in 40 gradient, around 4.5 to 5 metres away. This will terminate at the top of a 1.2 m3 hardcore filled soakaway.