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Hi all,

I’m soon to be starting a large diy project (for me) that I’ve been looking to do for quite some time. I’m going to be replacing the entire suspended floor in my lounge as the joist are basically laid on only a course high wall with no foundation and no dpc which has caused all of the joists to rot. Planning is being sought as it’s a listed building (circa 1740’s) and I’m planning on removing the entire floor structure and excavating the area to provide a minimum void depth of 150mm. Beneath that will be a dpm and 100 concrete covering. I plan to put in honeycomb walls to support the new joists and telescopic air vents as the floor is below external ground level so there’s no other way of ventilation. I’ll be working with a BCO once I have planning permission so will have everything confirmed by them, but till then, I can’t help but try and square a few things way in my mind that I hope to get some advice on?
Are honeycomb walls to support the new joists suitable over wall plates and hangers in a house circa 1740’s?
What size foundations depth depth x width would I need for honeycomb walls?
What distance should they be from the walls to allow for adequate airflow? And where the fireplace is, would 3 shorter walls (1 in front and 1 either side) be appropriate?
I’ve used a span calculator and 38 × 195 and 400 centres appears sufficient. Do you think that is adequate for this? It won’t support any structure above the floor except the floor itself.

Thanks very much for you help and expertise. Want to make sure I can get this well thought out and planned before starting.

Im more interested in the attitude of the conservation officer. Do they let you alter the method of construction in listed buildings? At what point do you have to notify planning or apply for lbc when working on listed places, new curtain rail, replacement internal door, roof repair etc etc?
Have you had a chance to check out any span tables for timber joists? Id have thought with those dimensions if you are reduced digging anyway you may get away without an intermediate support with soke decent depth joists

oz0707 wrote: ↑Mon Nov 06, 2023 7:35 pm Im more interested in the attitude of the conservation officer. Do they let you alter the method of construction in listed buildings? At what point do you have to notify planning or apply for lbc when working on listed places, new curtain rail, replacement internal door, roof repair etc etc?
Have you had a chance to check out any span tables for timber joists? Id have thought with those dimensions if you are reduced digging anyway you may get away without an intermediate support with soke decent depth joists

I wouldn’t be altering the existing method of construction. It’s a suspended timber floor now so won’t be doing anything different. Planning has gone in for a number of upgrades; windows, new front door, flooring throughout. It’s where you’re altering the building I believe, wouldn’t need it for a lick of paint or a new shower head. The joist depth I’ve looked at are correct, but I’ll need to dig out for 150mm void and 100mm concrete pad anyway. Will get this drawn up when I get approval. Can I used ledger for this so the weight of the joists transfers to the wall or would it be better to have it on sleeper walls? Just conscious on the age of the house and all that additional weight on a party wall

Id be going ledger plate on existing wall if it were me minimum disturbance