Raise ground floor level in an old church

[Jimbobjones]

I live in a converted church and I'm planning to raise the ground floor level significantly as the windows are too high up. With a solid concrete floor, internal block walls, and 30" stone walls this is a great opportunity to add some insulation and make it less of an ice box.

I want to add around 10-14" (TBC) over the whole ground floor living area 90sqm (hallway, 4 rooms, toilet, bathroom) I'm looking for some opinions on my proposed floor buildup:

• Level the existing concrete subfloor where needed (as level as I can make it)
• 1200 DPM lapped up to skirting height
• 100mm EPS100 (e.g Jabfloor100 £10 sqm)
• 100mm EPS100 
• 100mm EPS100 (overlap all joints)
• Vapour barrier
• 22mm T&G P5 chipboard (glued joints, floating floor)
• Carpet in rooms / vinyl sheet roll in bathrooms

Things I'm not sure about:

1. Installing EPS:
   1. Foil tape all the joints? 
   2. Does each layer freely float on the layer below?
   3. How should I cut the insulation around internal doorways; do I notch and run a continuous bond, or do I cut a break at the door threshold?
2. Support areas:
   1. Where should I have a timber frame; Under the shower tray and toilet?
   2. Do I do anything different on corners to add strength?
3. Services:
   1. Can I run anything in the insulation layer (between DPM<>vapour barrier)? Not water pipes or wires. Soil pipe? Shower waste?
4. Building Control (Wales):
   1. When do I need to get them involved?

 

Will gladly buy you a drink if you can help me out, Yaki da!

Edited October 20, 2023 by Jimbobjones

[jayc89]

Take a look at a glasscrete floor. It uses foamed glass as the DPM and insulation layer and is far more forgiven in period properties, especially those without a DPC. It's typically finished with a NHL5 slab, which you can run your UFH pipes in, although a concrete slab would work just as well. 

[Jimbobjones]

Unfortunately the property already has a concrete floor that must have been poured as infill when it was converted, and the block internal walls were built up from this base. Therefore I don't think breathable floors like glasscrete/limecrete would be of any added benefit as the damage has already been done. If the subfloor was rammed earth then I'd certainly be looking at this opption for the reasons you stated.

I'm also going to avoid UFH as it wouldn't be able to heat the space sufficiently, I'd still need lots of radiators. I'm hoping a floating floor and carpets would be 'good enough' compared to the current toe freezing situation

Edited October 20, 2023 by Jimbobjones

[jayc89]

12 minutes ago, Jimbobjones said:

Unfortunately the property already has a concrete floor that must have been poured as infill when it was converted, and the block internal walls were built up from this base. Therefore I don't think breathable floors like glasscrete/limecrete would be of any added benefit as the damage has already been done. If the subfloor was rammed earth then I'd certainly be looking at this opption for the reasons you stated.

I'm also going to avoid UFH as it wouldn't be able to heat the space sufficiently, I'd still need lots of radiators. I'm hoping a floating floor and carpets would be 'good enough' compared to the current toe freezing situation

 

Do you know when it was poured and/or how deep it is?

 

Have you done a heat loss calc? I'm in an 1850s building and we fitted UFH, worked well before I installed a wall insulation, even better since I have. 

[Jimbobjones]

We think late 90s based on what old planning docs I can find

I haven't done a calc yet for every room, but did a fag packet estimate for the biggest room as things are now: 150W/sqm and I currently have oil fired condensing boiler.
I could also drop ceiling and add wall insulation to bring the heat loss down but I still think the radiators would be needed - given all that and the cost of UF plumbing and screeding I just don't think its worth it. The pain of retrofitting

[Gus Potter]

On 20/10/2023 at 16:03, Jimbobjones said:

I live in a converted church and I'm planning to raise the ground floor level significantly as the windows are too high up. With a solid concrete floor, internal block walls, and 30" stone walls this is a great opportunity to add some insulation and make it less of an ice box.

I want to add around 10-14" (TBC) over the whole ground floor living area 90sqm (hallway, 4 rooms, toilet, bathroom) I'm looking for some opinions on my proposed floor buildup:

• Level the existing concrete subfloor where needed (as level as I can make it)
• 1200 DPM lapped up to skirting height
• 100mm EPS100 (e.g Jabfloor100 £10 sqm)
• 100mm EPS100 
• 100mm EPS100 (overlap all joints)
• Vapour barrier
• 22mm T&G P5 chipboard (glued joints, floating floor)
• Carpet in rooms / vinyl sheet roll in bathrooms

Things I'm not sure about:

1. Installing EPS:
   1. Foil tape all the joints? 
   2. Does each layer freely float on the layer below?
   3. How should I cut the insulation around internal doorways; do I notch and run a continuous bond, or do I cut a break at the door threshold?
2. Support areas:
   1. Where should I have a timber frame; Under the shower tray and toilet?
   2. Do I do anything different on corners to add strength?
3. Services:
   1. Can I run anything in the insulation layer (between DPM<>vapour barrier)? Not water pipes or wires. Soil pipe? Shower waste?
4. Building Control (Wales):
   1. When do I need to get them involved?

Like your post and love old buildings like this. What you propose is also easily reversable, you're being a good custodian.

 

I would give the EPS a miss and spend a bit more on 150mm thick PIR for the following reasons:

 

1/ Your concrete floors probably will be well off the level and you will spend ages getting this right.

 

2/ EPS particularly Jablite compresses a lot before it carries the declared load... localised loads around shower trays / brittle finishes etc

 

3/ The labour time in fitting three layers is hard going.

 

In summary by all means float your floor but I would not use Jablite or similar.When floating a floor use loads of glue and have some concrete blocks etc to hand to weigh it down while the glue sets. Leave a gap round the edge of the floor for movement.

 

Do one room first and see how that works in terms of your costs and time.. best to do it yourself if you can as you often get a better job.

 

Say you have the 10" (250mm) as the least thickness. What about using (100mm thick layer)  type 2 sub base.. it is often what we call plastic but we can use this to our advantage.. this binds together quite well with a whacker plate ( moisten if need be with a light spray of water), blind that with a bit of soft sand. The reason for the soft sand is that the insulation is often not flat.. has bows in it so the only dead weight you have to hold it down is the T&G flooring.. you'll get a bouncy floor. You can sweeten out the sand blinding a bit and bed the insulation to some extent.

 

For greater depth just increase the depth of the type two.

 

If you have a shower tray, often in the corner of the room then you can fix a batten with DPC behind to the wall to support the edge of the flooring.. yes not ideal but it will stop the floor dropping and the shower tray leaking. You can run water pipes and waste pipes in the insulation and in the blinding layer.. but avoid electrical cables unless in a duct. I have cables in my UFH concrete floor but they are in ducts and the heating pipes are kept away from the cables.

 

In terms of BC. Strictly speaking you are adding load to the floor but if pulled up you could probably justify it is ok.

 

Some things but not all.. I would check are:

 

1/ If raising the floor will that mean some of the glazing is now below 800mm if so glass needs to be safety glass or have protection.

 

2/ Do you have any stairs.. are you going to make the rises uneven and cause a non compliance?

 

3/ Is there anything you have not told us in terms of how the walls breathe? Be aware that when you introduce insulation to an old building it can shift dew points  etc.. best to just check before carting on.

 

One main thing is to put in plenty perimeter insulation.. I would try and go for 50mm and take this right down to the existing concrete floor. If you keep the dumpling of soil a bit warmer inside the external walls this will deliver a surprising benefit. you can see the effect this has to some extent when you look at the U value tables for insulated solid floors.. it's called the perimeter vs area ratio.. a lot of heat is lost around the perimeter.

 

 

 

 

 

 

 

 

 

 

 

 

 

[saveasteading]

I'd look again at ufh.  A major advantage is the comfort level from having heat under your feet and low down. Yes heat rises but that will apply to any source, and from rads you may get no benefit at all.

 

What @Gus Pottersays about perimeter insulation, I agree with. I believe the benefit is greater than the building regulations recognise and especially so with exposed stone walls as you will have.

 

For fill, a thin top screed will spread the load  on eps then you can finish with anything you choose.

Eps is half the price and half as good as pir, but that suits your need for depth.

After about 200mm there are diminishing returns on insulation.

 

It depends where you live, but there is probably a stone fill that is much cheaper than type 2.  Ask the quarry. Fill sand, scalpings, or it may have a local name. Crushed concrete or hardcore likewise. That will get your fill up to rhe height you need for eps to sit on.

I would tape all joints. It closes any air gaps and keeps everything in place better. With very thick eps slabs staggered, they might sit nicely enough without.

And use planks for moving around, to protect the soft eps.

 

[Jimbobjones]

Thank you @Gus Potter for all the considerations (matches my list, hopefully the only changes I will have is moving sockets and redoing all the doorways...). Perimeter insulation did not make my list so thanks for pointing out, I thought this was just for screed. 

Thanks @saveasteading for the cheap fill tip, I've checked with the local quarry website and they seem to have 7x different fill mixes so I'm sure one of these is the budget special. I'm reluctant to add a lot of stone build up due to my access; I could potentially go with a bulk tip but no doubt this would cause tutting in the village especially if we get more rain like last week. Alternatively lots of bags is just not worth the cost IMHO, would rather just fill it up with more insulation.

I'm going to get some proper room measurements and stop working on the back of an envelope, then reassess all options