Barn conversion on five acre plot in Northamptonshire

[Owain1602]

Hello all,

 

I've been a member here for a while, trying to learn as much as I can from reading any mildly relevant thread.

 

We recently purchased a 5 acre plot of land in open countryside, on the land is a barn which has approval for conversion under Class Q (expires April 26). The ideal scenario would be to build an efficient timber frame house on a passive slab, after demolishing the existing portal steel frame (current barn does not have a concrete floor).

 

We put in a pre-app to demolish the steel frame (keeping to the original footprint of the barn), and were told the local plan has policy that Class Q approval is not considered a fallback for a new-build dwelling, as such, it would not be supported (although this policy does not appear in the new emerging local plan!). Our architect spoke with the planning officer, and discussed the idea of wrapping the existing steel frame within the timber frame (means extending beyond the original footprint by ~350mm), and apparently was told that this would be supported via a full planning application. So here we are, finalising details of our full planning application, which now needs to include the full BNG calculations and report.

The deadline for needing to start implementing the existing Class Q is fast approaching, and if we're knocked back with this full planning application, we'll need to resubmit for Class Q (under the old regulations, before May 25) which should restart the 3 year clock. 

 

I have been an engineer myself for nearly twenty years, technically leading projects in the automotive, formula one and aerospace industries. My background was originally in numerical simulation of combustion thermodynamics (CFD), but now work on a fairly broad range of topics related to high voltage systems, battery thermal systems, controls and algorithms. Don't ask me anything about a domestic heat-pump control system though!

 

Nice to meet you all, I'm not sure I'd have the confidence to embark on what we're doing without the invaluable expertise and experiences I've read about on this forum. 

 

[Alan Ambrose]

Well congrats. BTW, if this is a self build, why do you need to do BNG?

[Owain1602]

Thanks very much Alan.

 

My understanding is that self-build exemption does not apply if the site area is greater than 0.5 hectares.

I'm interpreting information from here:

https://www.gov.uk/guidance/biodiversity-net-gain-exempt-developments

 

[Alan Ambrose]

Ah good point. I guess that new self build 5 acre / single dwellings are fairly rare and the reg was mainly written for larger developments of multiple custom builds, but it seems you are still caught. As there was some recent chat here on self builds being potentially trapped by BNG in future, I’m interested in how that all goes for you. And I’m sure we would all love to see some images of the plot and your designs when you’re ready.

[IanR]

Hello and welcome,

 

2 hours ago, Owain1602 said:

Our architect spoke with the planning officer, and discussed the idea of wrapping the existing steel frame within the timber frame (means extending beyond the original footprint by ~350mm), and apparently was told that this would be supported via a full planning application.

 

Sounds like your LPA is taking a pragmatic approach, which is as much as you can hope for. Look forward to seeing your plans once you are ready to share.

 

2 hours ago, Owain1602 said:

The ideal scenario would be to build an efficient timber frame house on a passive slab, after demolishing the existing portal steel frame (current barn does not have a concrete floor).

 

Hopefully keeping the portal frame has not put you off the passive slab, depending on finished floor level versus the height of the pads under the columns there's a bit of extra detailing to do, but it is all "doable". I worked through mine with Advanced Foundation Technology Ltd and came up with a neat solution dove tailing the two together so they have some previous experience which may be useful to you if you've not already settled on a supplier.

 

Have you thought of construction method for the timber frame? While the existing portal frame is quite an open structure, keeping the purlings in place (to keep teh LPA happy that it's a conversion) does make it awkward to crane a panelised system into place. I settled on a stick built solution but went with an I-Joist structure to allow lots of insulation.

 

Good luck with your planning app.

[LnP]

1 hour ago, Owain1602 said:

Thanks very much Alan.

 

My understanding is that self-build exemption does not apply if the site area is greater than 0.5 hectares.

I'm interpreting information from here:

https://www.gov.uk/guidance/biodiversity-net-gain-exempt-developments

 

Take a look at the de minimis exemption - habitat impact of less than 25 m2 of area habitat and 5 m of linear habitat. If the new building is on the footprint of the old one, that should exempt you.