Insulating my cellar ceiling

Bluey87

So on Friday I had my loft insulated, a difficult job as we have some suspended ceilings which have been installed over old lathe and plaster vaulted ceilings so access is extremely difficult. As they were leaving after successfully completing the job (adding 300mm of Knauf loft roll) I asked the boss to look at our cellar which is a traditional lathe and plaster celling with what looks to be joists of around 150mm, if not slightly more.

My plan is to cut away the old lathe and plaster in the cellar, carefully, to avoid the absolute breaking loose of hell that comes along with L&P and then check and vac all joists, clean them up so we can install insulation.

Questions:

1. He said that they would use the same roll that they installed in the loft. Would this be suitable for between joists in a cellar?

2. He stated that they would hold it in place with netting attached to the joists. Would it not need some form of vapour membrane or would the netting do that job? Similar to the system used and written about by Ecological Building Systems (https://www.ecologicalbuildingsystems.com/post/best-practice-approach-insulating-suspended-timber-floors) although I feel their system is best installed from above, which isn't possible without removing all our floor coverings. 

3. What do we do when we get to the stone walls of the property? Do we need some sort of barrier between the insulation and the stone wall?

The cellar is relatively dry and it has good airflow as it has old single pane windows, which are draughty, so I intend to replace these with more modern units but I do see them as a bit of a positive since they allow air to flow in the space.

I just want to make sure that I am 100% clued up so that I can make some informed decisions.

Couple of pics attached, you can see where some L&P was chopped out when we installed the new boiler and ran some new heating pipes to other parts of the house.

Thanks in advance.

Eldi_Dos

The first thing you want to do before planning any work in that area is get the wall and ceiling coatings tested.It could be Artex of a certain vintage and if so that will need to be taken into account how you go about the work.

What are you wanting to gain from adding isulation down there, make the rooms above warmer or make the celler warmer?

Bluey87

It just looks to be the same as the other areas, old lime plaster over lathe but we’ll look into that. 

My intension is to stop all the draughts and cold seeping up into the living areas, the image I posted is under the living room and it also has the cold slab in it. That window is single pane and has some hit and miss style slots which have a light well with a large cast iron grate over it. 

I think I’d like to replace the window with a new one too with double glazed units. 

It’s a very cold cellar and most of the ceilings are lathe and plaster. 

GDB2222

Why not just fill all the holes, possibly with expanded foam, and then put solid insulation in? I don’t see why you want to take away the old ceiling? 

I’d avoid flammable insulation, so I’d be looking at rock wool perhaps, but you might want to consider access to all your pipes. 

Bluey87

Everything I read about solid insulation (PIR) is that it doesn't allow any level of breathability so you end up with condensation against the wooden floor underneath and potential rot to timbers.

Also its very hard to get it to fit without leaving lots of gaps, regardless of expanding foam used to fill gaps and extreme care and attention to fit it perfectly as the timbers in houses like mine (Built in 1860 - not listed) are rarely at regular intervals across the span of a floor, hence the idea of using a product with more flexibility that fits the contours of the existing substrate.  

ThisIsWeird

Worth insulating under the floor of the room above? Surely, yes.
Worth fitting DG windows to the cellar? Hell, no. At least not unless you are planning to convert it fully into a habitable space, but that will mean major work - full tanking, insulation, heating, controlled ventilation, and all that malarkey.
I presume you don't plan to do this? At least, not yet? In which case, leave the cellar as draughty as it currently is - that's what keeps it acceptably dry.
Yes, test that plaster and ceiling paint for nasties - good call. Then mask, goggles, full gear, and remove.
Amusingly, the best form of insulation to then add between the joists would likely be spray-foam, as it would draught-proof the floorboards, add terrific insulation, and also help lag any pipes. It's just far too controversial to consider, alas.
So, yes, the proposed solution is fine - stuff loft insulation firmly up there, and secure with mesh. 

The good thing about loft insulation is that it breathes, but actually you shouldn't have any issue with condensation in there anyway - it will always be the warmest surface in the cellar, so the last place to cond.

The only drawback with loft insulation is that it's unlikely to stop draughts coming through, just reduce them. The easiest way, if you can lift whatever floor coverings you have in the rooms above, is draughtproof paper all over the floor, and mastic under the skirting boards. Failing that, I guess cut joist-wide sheets and try and position them from underneath against the boards, and then pack the insulation under it - awkward.

As for the joist-wall gap, just stuff insulation tightly up there using a stick.

 

GDB2222

https://forums.moneysavingexpert.com/discussion/5950847/spray-foam-insulation-for-underfloor-areas-of-the-house

Maybe worth a look. 

GDB2222

Bluey87 said:

Everything I read about solid insulation (PIR) is that it doesn't allow any level of breathability so you end up with condensation against the wooden floor underneath and potential rot to timbers.

Also its very hard to get it to fit without leaving lots of gaps, regardless of expanding foam used to fill gaps and extreme care and attention to fit it perfectly as the timbers in houses like mine (Built in 1860 - not listed) are rarely at regular intervals across the span of a floor, hence the idea of using a product with more flexibility that fits the contours of the existing substrate.  

What sort of floor covering do you have? 

It’s a bit of a trade off between allowing air circulation and insulation, but I agree that you don’t want rotted wood. 

ComicGeek

IMO this is the best source of information for this building type https://historicengland.org.uk/images-books/publications/eehb-insulation-suspended-timber-floors/

Chickereeeee

Bluey87 said:

So on Friday I had my loft insulated, a difficult job as we have some suspended ceilings which have been installed over old lathe and plaster vaulted ceilings so access is extremely difficult. As they were leaving after successfully completing the job (adding 300mm of Knauf loft roll) I asked the boss to look at our cellar which is a traditional lathe and plaster celling with what looks to be joists of around 150mm, if not slightly more.

My plan is to cut away the old lathe and plaster in the cellar, carefully, to avoid the absolute breaking loose of hell that comes along with L&P and then check and vac all joists, clean them up so we can install insulation.

Questions:

1. He said that they would use the same roll that they installed in the loft. Would this be suitable for between joists in a cellar?
Yes


2. He stated that they would hold it in place with netting attached to the joists. Would it not need some form of vapour membrane or would the netting do that job? Similar to the system used and written about by Ecological Building Systems (https://www.ecologicalbuildingsystems.com/post/best-practice-approach-insulating-suspended-timber-floors) although I feel their system is best installed from above, which isn't possible without removing all our floor coverings. 
A vapour membrane should be on the warm side of the insulation, presumably the room above. So, lay it on the room side, under whatever floor covering up you have - although personally I don't think it is that important for floors. I would rather not cover the joists from below in vapour proof membrane.
To support the insulation from below, I used air permeable membrane, as it let's the floor breath, allows vapour to pass through, but blocks drafts.

3. What do we do when we get to the stone walls of the property? Do we need some sort of barrier between the insulation and the stone wall?
I would suggest a water proof/vapour proof membrane between wall and insulation.

The cellar is relatively dry and it has good airflow as it has old single pane windows, which are draughty, so I intend to replace these with more modern units but I do see them as a bit of a positive since they allow air to flow in the space.
You could have trickle vents

FreeBear

First point, it is a plaster and lath ceiling - A lathe is a completely different beast and can weigh several tonnes.

Taking down a plaster & lath ceiling is an extremely messy job, so wear disposable overalls and a good quality dust mask when doing the job. Spraying the air with water helps to keep dust levels down..

I would recommend insulation batts rather than loft insulation type materials - A little more rigid. You'll still want netting to support the stuff. A waterproof membrane around the perimeter will stop water wicking from the wall in to the insulation. Steer clear of any spray foam - It is very difficult to remove should you find there is a problem. It can also hide any developing issues, and the first you know is when something fails. At least with batts, the stuff can be pulled out without causing further damage.