Woodworm in the floor joists...

[overlander matt]

OK thanks for the thoughts on the lime mortar for the wall. I'm in two minds about what to do so will have a chat with our joiner when I see him soon. The question is what type and size of timber to use for the repairs if I do go that route given the irregular size of the joists.

There is plenty to do elsewhere for now and I keep putting off writing a heritage statement for the LBC...

 

[george2019]

That's a modern specification though. It is neither necessary nor required for a suspended floor to function.

It's to keep the moisture content of the timber low enough to prevent rot, the reasoning applies equally to historic and modern construction.

Even if there was no ventilation and the air was at 100%RH, the resulting moisture content in pine will be about 23% at 22C which is too low for fungal spore germination. Ventilation might help keep the moisture content low enough to dissuade insect attack, but in pre-treated modern timber there is no risk of attack as long as it doesn't get wet.

My point is there isn't any reasoning: it's proscribed thinking from the 1950s/60s/70s when pre-treatment was rare and poor quality timber with a high sapwood contents was more routinely used. Smacking holes in old buildings to meet modern ventilation requirements dating from a period of history where risk was higher is pointless. There are plenty of Victorian floors without modern ventilation have not suffered at all.

I'm not saying its' a bad thing to do if you have the option, but is not a requirement and it should not be viewed as necessary in all situations (essentially: it's not what you are presenting, it's how you are presenting it).

There's certainly a lot in the regulations that I disagree with (foundation depths being one... often have to convince builders not to underpin old buildings. An expensive and pointless activity most of the time). I'd never thought about the ventilation as being other that reasonably sensible - for every OK Victorian floor, there's plenty with tarmac-covered air vents which have rotted. Have you any more information I could read up on this subject?

 

[MatthewC]

Interestingly, I had a visit from a structural engineer on Friday to look at a number of problem areas in the building. On seeing the floor joists he thought they were a bit far gone and asked 'why bother trying to repair them?'. So I wonder is he right or are the joists worth trying to save as I have so far assumed?
<snip>

I fixed a suspended floor in my lounge (see my blog for 2011 - blue spot on Contact button right), although I don't think it ever looked as bad as yours! I think I did pretty much what you are suggesting - replaced a single complete joist (rotted as alongside a damp wall) with modern timber, repaired a lot of rotted joist ends with modern timber, re-built a supporting wall with new air spaces, cleared the existing external airbrick and added a floor vent at the corner farthest from the external vent. Finally had to replace about 4 sq m of boards as the ends had rotted (so they were too short by inches) with reclaimed pine (annoyingly planed so a bit thinner than the rest). I also found that a lot of boards were different widths so re-using as many as possible was a conumdrum...

Requiring consent for air bricks seems a bit extreme, though if you’re making an application for other items then I suppose it’s easily added.

I'm confident my CO would expect me to apply for consent for airbricks. I certainly require it for an extractor fan vent and I've been told there is no guarantee I would get it.

An extractor fan (or a gas boiler outlet) is far more modern than a simple airbrick. Even my picky CO did not refuse the boiler exhaust on my application, and I don't think I ever mentioned the extractor outlet (flat on the wall) as it never occurred to me.

Matthew

 

[overlander matt]

To add a bit more to the thread, our local CO suggested that adding ventilation would not be necessary in our case. A Historic England report was referenced which concluded that removing the source of damp was key to preventing rot in suspended timber floors.

I have now dug out the sub floor, clearing out the general debris that accumulates over the years and rebuilt/repaired the walls using lime-based mortar. I have now repaired most of the joists - just two to go and these felt reasonably firm suggesting they have been replaced previously.

Did you apply for LBC in your case Matthew to replace the joist? I fear I might be making an application every other week if so...

Thanks for the information. Having a non-springy floor is quite satisfying.


Matt

 

[george2019]

To add a bit more to the thread, our local CO suggested that adding ventilation would not be necessary in our case. A Historic England report was referenced which concluded that removing the source of damp was key to preventing rot in suspended timber floors.

Reading their report, the research they conducted is whether having openings actually cause an airflow and the rest is a discussion on historic development and performance of ventilation. But airflow isn't the primary reason of a sub-floor vent, it's to allow high humidity air a pathway to low humidity air (and vice versa, but so long as there is some drying out, timber is protected) via, as a minimum, diffusion. There is a clear route for humidity into a sub-floor area - it can come from above or from the ground below. Historically, buildings never needed vents because the floor boards and rugs allow a pathway for humidity to escape, but with air tightness and draft reduction being a concern these days, I consider a separate sub-floor vent to be a prudent measure.

Likely, sitting a treated timber on a dry substrate off the ground and sealing it up will be fine for a long time, but I still will encourage existing vents to be maintained I think!

 

[MatthewC]

...A Historic England report was referenced which concluded that removing the source of damp was key to preventing rot in suspended timber floors..

There's a surprise! Do bears ...? :roll:

Did you apply for LBC in your case Matthew to replace the joist?

No way! I don't know if I should, but after the trouble I had with the CO (who never visited but was keen to be strict despite the ignorance of the situation) I wasn't going to ask. One thing I learned from the process was to know when to ask and when to not even mention something. Of course, because the CO never visited, they had no idea what the situation was before I started. 8)