Timber framed extension (uk) - damp course too low

[renovo]

Hello all,

My mum is having a timber framed extension built on to her house (side extension).

The extension has a utility room at the back and garage at the front.

The damp course around the utility matches the house as you would expect.

However, the garage wall drops down 150mm where the damp course is barely 10mm above ground.

The builders said a garage floor has to be 150mm lower than the house which turns out to be correct (some fire regulation).

While the floor has to be lower I don't see why the wall should be lower. In my view it should match the height of the extension with only the floor dropping.

The builders have accepted that the damp course is low and said they would put in drains.

-----

I would love to hear your opinion on this. My view is either 2 things should happen:

1. Pause construction and have the plains changed to a habitable room instead of a garage (my mum does not intend to use the garage as a garage, only storage).

2. The walls of the garage should match the wall of the utility so damp course follows through. This will not effect the concrete floor which will remain 150mm lower as the utility will be insulated and screeded.

I have attached some photos and would love to hear your opinions.

Many thanks.

 

[renovo]

The last photo shows how the wall/damp course drops down between the rear utility and front garage.

The first few photos show how low the damp course is.

Many thanks

 

[^woody^]

Garage floor should be lower or a raised step 75mm between the garage and the house.

The DPC does not need to be lower.

A timber frame (where the frame is the external wall and is clad) must be at least 150mm above the external surface level irrespective of the DPC level - although the two are normally the same.

What do the plans say?

 

[renovo]

Garage floor should be lower or a raised step 75mm between the garage and the house.

The DPC does not need to be lower.

A timber frame (where the frame is the external wall and is clad) must be at least 150mm above the external surface level irrespective of the DPC level - although the two are normally the same.

What do the plans say?

Thank you. So you are saying that the DPC level of the garage is unacceptable?

I will be checking the plans in detail today. But whatever the plans say I can't accept the DPC level of the garage. it is going to fail over time as it is now.

What you are saying has confirmed my thoughts. The way it's been done is incorrect and cannot continue.

if building inspectors saw the current DPC level surely it would fail?

 

[^woody^]

if building inspectors saw the current DPC level surely it would fail?

Not necessarily.

The regulation is to prevent moisture getting to the inside, and there are several ways to achieve this other than the oft-quoted 150mm to external ground level.

Of more importance with timber frames, is to ensure the detail and quality of construction is good enough to ensure long life and avoid premature rot at ground level. This is not covered by building regulations - which just cover a very basic standard. So there needs to be extra care with the frame and cladding at the base to ensure that the frame and cladding is not damaged by rising or splashing moisture, that there is ventilation, and that water is suitably drained from the cavity and dispelled from the face of the cladding.

 

[renovo]

To quote you:

A timber frame (where the frame is the external wall and is clad) must be at least 150mm above the external surface level irrespective of the DPC level - although the two are normally the same.

The base timber plate is about 20mm above ground level.

 

[^woody^]

Timber frame construction, is a bit specialist and ideally, requires experience and knowhow to get right. It's not like just knocking up an internal stud wall.

Ideally the designer should detail everything properly for the builders to follow. Alternatively, the builders should be experienced enough to know best practice.

Most of the problems with a timber frame occur a few years after the jobs been signed off by building control and the builder long gone.

 

[renovo]

Timber frame construction, is a bit specialist and ideally, requires experience and knowhow to get right. It's not like just knocking up an internal stud wall.

Ideally the designer should detail everything properly for the builders to follow. Alternatively, the builders should be experienced enough to know best practice.

Most of the problems with a timber frame occur a few years after the jobs been signed off by building control and the builder long gone.

Of course but a frame only 20mm off ground level screams a big problem to me. Hence why i am here to get more opinions.

I am trying to help my mum avoid paying £50k for an extension which is going to fail in future years.

 

[renovo]

Not necessarily.

The regulation is to prevent moisture getting to the inside, and there are several ways to achieve this other than the oft-quoted 150mm to external ground level.

Of more importance with timber frames, is to ensure the detail and quality of construction is good enough to ensure long life and avoid premature rot at ground level. This is not covered by building regulations - which just cover a very basic standard. So there needs to be extra care with the frame and cladding at the base to ensure that the frame and cladding is not damaged by rising or splashing moisture, that there is ventilation, and that water is suitably drained from the cavity and dispelled from the face of the cladding.

You are way off the mark with that. I have done a lot of research since posting this and spoke to builder friends. A DPC should always be at least 150mm above ground. It cannot be replaced by another method, it simply has to be done right. Then of course you have other building standards/damp protection methods you can use.

The construction has now been paused and a building inspector will be checking the DPC which I will make very clear has been done badly.

 

[^woody^]

You are way off the mark with that. I have done a lot of research since posting this and spoke to builder friends. A DPC should always be at least 150mm above ground. It cannot be replaced by another method, it simply has to be done right. Then of course you have other building standards/damp protection methods you can use.

The construction has now been paused and a building inspector will be checking the DPC which I will make very clear has been done badly.

I'm on the mark. I've done a lot of work, not just googling.

The requirement is to prevent damp ingress. How that is done does not matter. For instance, a tray can be used to allow a lower external DPC.

Google "level threshold" and tell me where the DPC is.

 

[renovo]

I'm on the mark. I've done a lot of work, not just googling.

The requirement is to prevent damp ingress. How that is done does not matter. For instance, a tray can be used to allow a lower external DPC.

Google "level threshold" and tell me where the DPC is.

I have also done work

I build £300k+ swimming pools, fully renovated my Victorian property and built a high end garden office alone. Not to mention I have many friends who are builders by trade. The only reason they didn't take it on was distance. They looked at the photos and straight away were concerned.

On new construction there is no reason to have the DPC under 20mm from the ground. If you think that's acceptable you're insane. There was 0 reason to have it this low.

It was so easy for them to build this correctly and have the DPC at 150mm. But for some reason you are defending such a dreadful decision and saying they can get around it. Simply not good enough.

In places that base timber plate is BELOW ground level.

 

[renovo]

It should be common sense but even the NHBC make it very clear:

10.1.5 Garage walls - NHBC Standards 2023

nhbc-standards.co.uk

"To protect the wall from rising ground moisture, a DPC should be provided at a level at least 150mm above the level of adjacent ground."

 

[^woody^]

"To protect the wall from rising ground moisture, a DPC should be provided at a level at least 150mm above the level of adjacent ground."

"Should" not "must".

NHBC standards are the lowest minimum and are really for the average Joe to pick up and build something to those lowest standards and conform. Your builder friends must only know this one base method, and can't be experienced in anything else.

This is the third time now, the requirement is to prevent damp from getting into the building. How that is done can be one of several ways.

Whilst the work mentioned earlier in the thread may well be sub-standard, that is different to the statement that "a DPC must be 150mm above ground level".

 

[phatboy]

You sound like a complete idiot to be honest.

Blah blah

You're pretty **** at accepting advice aren't you? If you know it all, why are you here asking?

I'd suggest ^woody^ is greatly more experienced than you, and he hasn't even billed you for his replies.

 

[renovo]

Bill me for his replies haha. What 2 contradictions and being completely wrong? Haha you guys are pathetic.

Just because he posts free content on your community does not make him experienced.

He said this wasn't a issue. Well building control disagree and they have now been forced to re-do the DPC following the block all the way through.

I had genuine good advice on another forum, I won't be returning here.