Hi, I want to use a pad and lintol design for a foundation, this to protect a nearby tree (it's for a single story extension). The pad at 200mm thick has to be a min 600mm below ground, I then presume I have to build up out of the ground to sit the lintols on. What is the best way to build up (block and concrete fill?) and do I have to sit a precast padstone on top of that for the lintol to sit on?
Pad and Lintol foundation arrangement
- Thread starter Tul
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Are you lintelling over a tree root? 
And what if a pad is required just where a root is?
Also wouldn't pads be more susceptible to ground movement caused by the roots?
Have building control OK'd this method - normally they would be more concerned about the foundations and not the roots
Also wouldn't pads be more susceptible to ground movement caused by the roots?
Have building control OK'd this method - normally they would be more concerned about the foundations and not the roots
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It hasn't got to BC yet, the design is from the SE and based on the Tree survey, it's a 500 to 1000 ur old Yew and planning won't let us do anything unless we can show the tree will be protected. If we meet a root we can protect with a split case. The ground has been stable for decades so we don't expect movement plus we are near the edge of the tree canopy so the structural roots are a max of about 2". I think the pad and lintol method is my one and only option, also prob the easiest as it has to be hand dug and no machines allowed due to soil compaction. So what is the best way to get from the pad up out of the ground, it's also a sloping site so pads/columns will have different heights to reach a common level.
Hasn't the SE specified the design?
You would build up off the pad with bricks/blocks, and then sit the lintel on with no need for a padstone.
I suppose a trench block would do, otherwise solid walls to the required thickness (or wider to work blocks/bricks) which would be easier than messing about with cavity walls and concrete fill
Sort out the finished ground levels and make sure the lintels are below this - set up some datums at each pad and mark the finished floor level (FFL), ground level and lintel level. Remember to always gauge down from the FFL in 75mm (one brick course) increments
You would build up off the pad with bricks/blocks, and then sit the lintel on with no need for a padstone.
I suppose a trench block would do, otherwise solid walls to the required thickness (or wider to work blocks/bricks) which would be easier than messing about with cavity walls and concrete fill
Sort out the finished ground levels and make sure the lintels are below this - set up some datums at each pad and mark the finished floor level (FFL), ground level and lintel level. Remember to always gauge down from the FFL in 75mm (one brick course) increments
Just to reiterate woody's post, make sure you get BC comment before you dig a hole.
Thanks for the input. The SE has drawn it out, it arrived the day he left for a 2 week holiday! There is a section drawing which shows the Lintels sitting on the pads below ground level. To me this is crazy because digging out the ground between pads for the Lintel defeats the object of using the pad lintel design. Am I right in thinking what I have to do is;
1) pour the pads to 600mm below ground.
2) build up out of the ground to a common datum for all the pads, using block/bricks.
3) set the ground beam intels out on the pads.
4) Build the walls up from the ground beam lintels.
The lintels would then be sitting up proud of the ground as if on stilts. The ground would then be made up to cover the lintels.
PS. Carlisle stayed up today great game first win in 12, who cares about foundations eh!
1) pour the pads to 600mm below ground.
2) build up out of the ground to a common datum for all the pads, using block/bricks.
3) set the ground beam intels out on the pads.
4) Build the walls up from the ground beam lintels.
The lintels would then be sitting up proud of the ground as if on stilts. The ground would then be made up to cover the lintels.
PS. Carlisle stayed up today
great game first win in 12, who cares about foundations eh!
By the way, what soil type do you have?
Hope it's not clay!
Having thirsty tree roots meandering beneath a structure is not something i would welcome.
Hope it's not clay!
Having thirsty tree roots meandering beneath a structure is not something i would welcome.
The soil is not clay as you think of it but Boulder Clay, common in the Lakes. It is extremely hard making a good base but trees have to shallow root for moisture, in my case the root area is massive but these are not large structural roots by the time they reach my project.
Is it OK for my ground beam lintels to sit on the pads up out of the ground?
Is it OK for my ground beam lintels to sit on the pads up out of the ground?
At such a distance from the tree, and with few significant roots, then would it not be possible to show that a normal foundation will have no impact on the tree, and so avoid faffing with pad and beam foundations?
That's why I previously asked what if there was a root where a pad needs to be - ie placing any foundation can impact a root, and so if you can put a pad and beam here, then why not a normal strip, and just take care with the excavation and throw in some polythene slip planes if need be?
Has your tree survey ruled out a normal strip foundation?
That's why I previously asked what if there was a root where a pad needs to be - ie placing any foundation can impact a root, and so if you can put a pad and beam here, then why not a normal strip, and just take care with the excavation and throw in some polythene slip planes if need be?
Has your tree survey ruled out a normal strip foundation?
Yes, a normal strip foundation has been ruled out. This is a very rare tree, the 1000 yr old Yew at Lorton and the 1500yr old one at Martindale are very famous and this tree is in the same league. If we push the point and even hint it might be under threat we will have a TPO slapped on, meaning £500 in surveys every time we want to prune a branch! Although logistically a pain the tree means a lot to me and I'm prepared to put in the effort and cost to protect it. The main concern in the survey is to preserve the moisture content in the soil, which also includes capturing the rainfall from the new roof area and directing it to a soak away upslope from the tree.
Thanks for the info by the way, I have been looking up trench blocks which if okey by BC will save backache. I presume a ground beam will be immune from frost damage?
Thanks for the info by the way, I have been looking up trench blocks which if okey by BC will save backache. I presume a ground beam will be immune from frost damage?
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