Conservatory Wall Footings Depth?

Frank99

My brother in law had his conservatory footings dug out yesterday but for the full height walls they have dug down 39 cm with a shovel, i'm no expert but with a glass roof weight i thought it had to be minimum of 60 cm/ 600mm deep.
He has been told by the builder that it is very solid soil and will only require to go down 4500mm which seems like a bit of corner cutting to me.
I see recommendations everywhere for digging between 600-900mm so have told him to ask for this.
I know it is an unregulated area and so they might be cutting a few corners thinking he doesn't know any better.
HELP?:mad::mad:

Doozergirl

For any footing to be solid it needs to be at least 1 metre deep and filled back with concrete by around 70cm. That is the nearest point at which you will find solid ground. If building control or a structural engineer were involved, they would dictate exactly how deep for the ground conditions.

With average house building it isn't about the amount of weight going down on the ground, it's about avoiding natural ground movement that occurs all the time.

You are absolutely right that it isn't regulated and those 39cm footings are why conservatories are cheap. Because they have no regulations to meet they don't even try.

Your brother isn't paying for metre deep footings. No one is trying particularly hard to pull wool over anyone's eyes. People just don't look or ask questions.

stuart45

The depth of a foundation depends on the ground conditions. For example 1 metre deep may not be enough in shrinkable clay with trees close by, whereas in areas of hard chalk such as the Sussex coast the digger sometimes struggles to get down to 1 metre.
It's usually best to go down to at least the level of the original foundation. Trench fill is a more modern method to avoid the cost of bricklayers in a deep trench.

Frank99

I'm devastated for him, costing 14k or so and after telling him about the footings i seem to have caused him a headache.

stuart45

One of the popular ways for building a connie footing is to build a single skin of brickwork up to DPC, and then concrete the floor and build the inner skin off the floor to form the cavity. Saves building 2 skins up to DPC, but in some cases allows moisture to penetrate at the base of the wall.
You can always tell him to drive a piece of 2x2 into the footing and show him it's not deep enough.

Frank99

stuart45 wrote: »

One of the popular ways for building a connie footing is to build a single skin of brickwork up to DPC, and then concrete the floor and build the inner skin off the floor to form the cavity. Saves building 2 skins up to DPC, but in some cases allows moisture to penetrate at the base of the wall.
You can always tell him to drive a piece of 2x2 into the footing and show him it's not deep enough.

Might well do that with the 2x2:T

Frank99

After he complained today he has now texted me to say the Company Surveyor has agreed to tell the builders to dig deeper footings, apparently the floor height has to be increased about a foot to match the house on top of the ground or at least this is what the surveyor told him as an excuse as to why they didn't go deeper.

stuart45

The ground floor level being higher does not mean that the bottom of the foundation can be raised by a foot. It just means that you need an extra 4 courses of brickwork to DPC,

Doozergirl

stuart45 wrote: »

The ground floor level being higher does not mean that the bottom of the foundation can be raised by a foot. It just means that you need an extra 4 courses of brickwork to DPC,

Indeed.

They're lying.

Frank99

I'm betting as they don't have a mechanical digger they're to lazy to go deeper, i'm gonna tell him to keep nagging them to go deeper or allow me and him to do it ourselves during the weekend storm.

stuart45

Frank99 wrote: »

I'm betting as they don't have a mechanical digger they're to lazy to go deeper, i'm gonna tell him to keep nagging them to go deeper or allow me and him to do it ourselves during the weekend storm.

Hope they are going to pay you. The gangs that put in the footings for connies are usually subbies, so it pays them to do the job as quickly as possible. Most people don't realize the correct depth they need to go, so usually they don't go down too deep.
Foundation depths on houses are much deeper nowadays(since the summer of 76), but before that a couple of feet was normally OK in good ground. Can also depend on whether you have any deep drains close by.