Subsidence in conservatory

[Inaquandary]

I need some advice please. I have a conservatory which is approx nineteen years old but it’s a good one put in by Zenith windows by previous occupants of my house. I’ve been here for the last thirteen years and it’s been fine.. no issues . But earlier this year a crack appeared between the brick wall and the house. The conservatory doors are misaligned too.
l‘ve had a builder round to look at it - from a reputable local company- who says the foundations need underpinning. I asked him about whether it was best to have it taken down and he said it was a good conservatory and would add value to the house if underpinned.
my concern is that if I go through building regs or insurance, my house value will go down and my insurance premiums rocket. if I don’t go through those routes and still have the underpinning done and I then sell the house I will not have a clear conscience
if I have it taken down then the costs of the removal and subsequent making good, is just over a grand cheaper than having it underpinned.
I really can’t decide which is the best route to go and hoping for some advice. money Is limited as I am now officially an OAP. I think my builder is fed up with me asking questions Please can you help me decide which way to go forward?

update.. have attached two new pics

 

[RonnyRaygun]

I wouldn’t underpin a conservatory. Would your buildings insurance even cover underpinning for a conservatory?

If you were able to claim, once underpinned as you know you will have difficulty with future insurance premiums and it may affect your sale as the value of the property will inevitably be affected.

Conservatories aren’t subject to building regulations so they are often built on minimally deep foundations, without consideration for the soil type or nearby trees etc.

Do you have trees nearby? Clay soil? Did the crack open up in its entirety or majority this year?

 

[Inaquandary]

The ground around here is clay.. there are two trees but they are about 25 foot away from the conservatory..the crack may have been hairline last year but opened up this year… got worse this summer… my insurance may pay out bout I’m reluctant to go that route for the reasons you suggested

 

[^woody^]

Why don't you just leave it?

If the foundations have moved due to this year's dry season, then they may well move back after the wet season.

Run some flexible mastic up the wall, likewise in white for the frame, and then relax

 

[Inaquandary]

Thank you for your replies.. am concerned this started early last year as there was a hairline crack running up.. early this year the crack between the brick wall and house opened to about one centimetre but doing the summer the gap has become bigger.. so the hot weather has made it worse but it was there last year.. I questioned my builder if the heat had affected it but he looked round the conservatory and said he didn’t think that was the cause and said that most conservatories did not have deep enough foundations .. the gap between the wall and house has deepened to approx an inch..as previously stated the doors to the conservatory are definitely misaligned now .They shut but there is a gap at the top of one side…

 

[RonnyRaygun]

An inch?! At the top of the dwarf wall?! That’s pretty significant movement!

25 feet away is close enough for trees to have a significant influence depending on the species and the volume change potential of the clay soil, especially considering the foundations are likely pretty shallow.

It’s the dry weather that causes an issue more than the heat. The trees still need to drink, and will continue to extract water from the clay, causing it to shrink.

It might close up a bit in the winter but unlikely it’ll close up an inch.

 

[Inaquandary]

So what’s my best bet? Should I get it underpinned? and risk devaluing my house if I sell or have it taken down and made into a patio area….. if I get it underpinned, am I likely to have the same problem in ten years or so? I’m a newly fledged OAP (though I don’t feel that old ) on limited funds so can’t afford any surprises in later years… my builder says that underpinning will push the wall back into place… I really don’t know what to do for the best

 

[RonnyRaygun]

If you aren’t selling imminently why worry? Do the doors still open and close? You might be able to realign the doors so that they continue to operate normally if they get any worse.

Underpinning won’t close the gap up so you’ll still be left with a crack and misaligned doors unless the crack closes up on its own in wetter weather.

 

[Inaquandary]

Tbh I have stopped using the doors as they are so misaligned.. the conservatory is nice but like all conservatories they get too hot in the summer and too cold in the winter.. my two cats love it but it’s totally unusable in the winter months

 

[^woody^]

If you are minded to underpin, don't let a builder loose on his own. Underpinning requires professional assessment by a structural engineer, to confirm if it's appropriate and then designed. And you don't want underpinning done and then the whole lot moves up when the ground rehydrates.

Also look at " resin ground injection uk " - put those words into Google. I'm not a fan, but others are, and it may be an option.

 

[noseall]

This connie was underpinned but it was futile as the plot had made-up ground around it.

Connie

• noseall
• 23 Nov 2019

The original ground level was some 1.5m down from original, so that even the underpinning was still on made up ground. It resulted in a rotation of the outer wall which affected the build-in joist hangers, causing them to fail.

 

[RonnyRaygun]

If you are minded to underpin, don't let a builder loose on his own. Underpinning requires professional assessment by a structural engineer, to confirm if it's appropriate and then designed. And you don't want underpinning done and then the whole lot moves up when the ground rehydrates.

Also look at " resin ground injection uk " - put those words into Google. I'm not a fan, but others are, and it may be an option.

Shouldn’t have an issue with upward movement as long as the pins are formed beyond the tree influence zone. Which they should be if the NHBC tables are followed. Best to carry out the underpinning following a wet winter when the gap has closed up as much as possible.

This connie was underpinned but it was futile as the plot had made-up ground around it.
The original ground level was some 1.5m down from original, so that even the underpinning was still on made up ground.

Piling would have been a better option but probably not cost effective for a connie (although, if insurance is paying…)
I did an insurance job on a new-build a couple of years ago (a house, not a conservatory) where due to the conditions beneath the foundations a piled raft was retrofitted, picking up every load bearing wall, inside and outside. I dread to think what the cost of this was and it must’ve been a nightmare to construct.

I guess Geobear might be able to do some kind of ground improvement for made ground too…

 

[Inaquandary]

If I do go through the route of underpinning the conservatory, will this stop all movement or will I have to underpin again in future years?

I really appreciate all your replies..

 

[George_engineer]

I wouldn't underpin a conservatory.

Traditional underpinning relies on brickwork arching and even then usually results in some movement of the structure. In a conservatory that could lead to broken glass, and damage to the dwarf wall. It would be for a contractor to say but I'd have thought it'd be more cost effective to take down the conservatory, dig new footings and rebuild it. At which point you'd be better off building a small extension to make it an all-year usable space.

Properly designed underpinning should be a one-time thing. I wouldn't do anything until the soil has reached a new moisture content equilibrium - this has been an exceptionally dry summer.

So with that in mind, I'd go for the 'fill the gap and wait' method.

 

[Inaquandary]

Thank you… I feel I’m mucking my builder around by my indecision on this..but my funds are limited and need to be spent wisely… perhaps I should put off a decision until the spring time when I’ve had more time to think about it and am better informed

I only have two choices - underpinning or removing conservatory.. unfortunately funds won’t stretch to having an extension built or a new conservatory