# Insulating under suspended timber floor - Options & Opinions on Tonzon Cushion



## thumbelina (22 Nov 2011)

Hi Everybody,

We are undertaking some renovation work in our home and one of the areas we are going to address is the level of insulation. The house is relatively old (1970ish) and the ground floor is built using a suspended timber floor.

I was reading a thread here today "*Insulation consultation*":

And can see two options:

(1) Lift floor, install mesh, insulate on top of mesh, (add air tight membrane), re-lay floor

(2) "Modern solutions will seek to remove the floor, install a concrete  slab over insulation on top of a radon gas barrier, with chemical DPCs  in the walls." - that sounds like it might not be the best way though "total agree, also concrete is a lazy option"

I was reading one of those home improvement magazines at the weekend and it had a feature/advertisement for a product called the Tonzon Cushion : (not allowed to post a link yet - google for "tonzon theromocushion")

It certainly looks straightforward to fit and is claimed to be a cheaper option.

Does anybody here have any experience / knowledge of this product - there is very little information on the internet about it and only one company in Ireland seem to supply/fit.

(usual disclaimer - no connection or affiliation to that company - just a customer looking for opinions)


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## lowCO2design (22 Nov 2011)

Tonzon- looks dodgy as i cant find an address, certification or any actually data other than stated values on the hard to navigate site.

option 1 or a variation is the way to go, but ensure there is no dampness + vents are open below floor to ensure adequate ventilation of moisture and radon etc. it may be easier to install a membrane instead of mesh but change both to something like [broken link removed]


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## onq (22 Nov 2011)

The link states that it is a variable vapour membrane that tries to prevent moisture getting past it into the insulation in winter and allows it back out of the insulation in winter
How does it "know" when its summer and when its winter and how long does an Intello membrane last in use?

ONQ

 [broken link removed]

 All advice on AAM is remote from the situation and cannot be relied              upon                                   as a defence or support -     in     and      of     itself  -         should       legal            action      be             taken.
 Competent legal and building professionals should be asked to advise in                                                Real Life with rights to        inspect     and      issue         reports    on     the            matters        at           hand.


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## lowCO2design (22 Nov 2011)

onq said:


> The link states that it is a variable vapour membrane that tries to prevent moisture getting past it into the insulation in winter and allows it back out of the insulation in winter
> How does it "know" when its summer and when its winter and how long does an Intello membrane last in use?


Proclima's no different from siga. any of the better brands, make similar claims

how about we call it what it's needed for: a vapour control layer/ air-tightness membrane. Any breathable properties are a bonus, when installing insulation between timber that can absorb and release moisture.

from the IAB cert the Intello product: 'will have a life comparable with other elements of construction in accordance with BS 7543:1992'


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## onq (25 Nov 2011)

I asked how these claims can be substantiated, not whether others make the same claims.

How can a membrane "know" when its Winter?


ONQ

 [broken link removed]

 All advice on AAM is remote from the situation and cannot be relied               upon                                   as a defence or support  -     in     and      of     itself  -         should       legal             action      be             taken.
 Competent legal and building professionals should be asked to advise in                                                 Real Life with rights to         inspect     and      issue         reports    on     the             matters        at           hand.


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## lowCO2design (25 Nov 2011)

onq said:


> I asked how these claims can be substantiated, not whether others make the same claims.
> 
> How can a membrane "know" when its Winter?


A good air-tightness membrane from a reputable manufacture will stop   water vapour entering your wall build-up, stopping condensation as the  internal air is reduced and is less likely to meet a cold material and  its due point on the way out.

There are also membranes that make statements along the lines that their   material (as well as air-tightness) offers a Gore-tex type system that   can regulate water vapour through the building fabric depending on the   season.. 

Using modern new materials does require a more careful assessment/   hygrothermal prediction before detailing. Computer simulation is now   considered far more accurate and appropriate than the long hand   calculations/ psychrometric chart reading done in the past.

The more I contemplate a poly..(can never spell them)material allowing a   'humidity variable diffusivity barrier' the more sceptical I become  but  there are timber products that deal with moisture similarly, and  I'd  tend to trust them more, I don't know why.. 

However, the principle is very real and has been used for thousands of   years, from mud & straw walls in Wexford, to rammed earth earth   walls from France to the Tangiers, or our Lime/stone built homes and   with the more recent revival/discovery of lime/plastered straw and   hemp-lime buildings - all actually providing a 'breathable' wall   structure not forgetting the Scandinavians who are doing all this for   just as long, but staying warmer! 

All the clever internal membranes in the world must be matched with   other suitably 'breathable' appropriate materials the whole way to the  outside  rain-skin..

here's one study from one the leading 'vapour active membrane' people
[broken link removed]

J Little has also done alot research into the area http://ukpassivhausconference.org.uk/sites/default/files/managing moisture_Joseph Little-1.pdf


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## onq (25 Nov 2011)

I totally accept your general comments and agree with them - breathabilityl properly anticipated and directed, can be a good thing.
I just don't understand this idea a "sentient" or knowing membrane able to tell the seasons of the year.
There are days in winter and summer where it is the same humidity and temperature.

Does the membrane take an average of the previous and next months weather the say "Oh its winter again" - I assume not.

Does it react to local differences between internal and external temperature and humidity - how can it sense them?
Is there a lag so these even out over time in the winter and summer and it takes a "stance" much like Lime Mortar?
I don't know - the nature of the construction in which these membranes are used suggests this isn't the case.
I'm probably missing something here LC02, but the claim doesn't seem to make much sense to me 

Thanks for that Joe Little link - I'll look at it this afternoon.


ONQ

 [broken link removed]

 All advice on AAM is remote from the situation and cannot be relied                upon                                   as a defence or  support  -     in     and      of     itself  -         should        legal             action      be             taken.
 Competent legal and building professionals should be asked to advise in                                                  Real Life with rights  to         inspect     and      issue         reports    on     the              matters        at           hand.


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## lowCO2design (25 Nov 2011)

I have no idea how the 'intelligent' element works



lowCO2design said:


> how about we call it what it's needed for: a vapour control layer/ air-tightness membrane.



as I said my preference is for wood fibre sheeting with similar properties to the membranes but they are not suitable in every instance just like the OP's


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## thumbelina (25 Nov 2011)

Hi lowCO2design,

That's a good point on the certificate on the Tonzon - I did try to track it down on the website myself but got a broken link. They mention a VCA certificate but that seems to relate to safety in construction.

Not that I know anything but it looked like an interesting solution - and the page in the magazine was really glossy so it must be good!

Anyway - back to my main question if you don't mind - can you give me a pointer to some diagrams / further info on that mesh based method and any rationale as to why I should pick that over the concrete slab approach?

Many thanks.


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## onq (25 Nov 2011)

You need to appoint a building professional to come and assess your building and comment on alternatives which you can get costed.
Underlying factors may be discovered during any inspection which might suggest one route could be better than another.
The building professional you need depends on what you want to do - total redesign or incremental update.


ONQ

 [broken link removed]

 All advice on AAM is remote from the situation and cannot be relied                 upon                                   as a defence or   support  -     in     and      of     itself  -         should         legal             action      be             taken.
 Competent legal and building professionals should be asked to advise in                                                   Real Life with rights   to         inspect     and      issue         reports    on     the               matters        at           hand.


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## lowCO2design (27 Nov 2011)

thumbelina said:


> can you give me a pointer to some diagrams / further info on that mesh based method and any rationale as to why I should pick that over the concrete slab approach?


concrete slab approach requires a sump, radon barrier/damp proof course insulation etc - imo it would be a far more expensive job, but then I haven't seen your house, so I cant say what you'll find when you lift the floor but if thats the sort of money you have to through around, Ill suggest something else: there's a product called Aerogel on the market it was developed by nasa and is 10mm thick with similar properties to putting in a good couple of inchs of regular insulation, its cost 25-30€ per Msq and could be laid with minimum effort under the existing floor boards

back to your your question 

http://www.nu-heat.co.uk/s.nl/it.I/id.453/.f[broken link removed]

see p45

do as ONQ suggests, get a professional in to assess the ventilation and condition of floor timbers etc.. before getting the trades in. good luck with it


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## onq (27 Nov 2011)

Hey LowCO2Design,

Found a local link for that material
[broken link removed]

Looks very interesting for someone I'm advising at the moment.
Have you any experience of it or know where its installed?


ONQ

 [broken link removed]

 All advice on AAM is remote from the situation and cannot be relied                  upon                                   as a defence or    support  -     in     and      of     itself  -         should          legal             action      be             taken.
 Competent legal and building professionals should be asked to advise in                                                    Real Life with rights    to         inspect     and      issue         reports    on     the                matters        at           hand.


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## onq (27 Nov 2011)

Okay - found the brochure [broken link removed].

A quick note - the Proctor Spacetherm sboard has plasterboard facing.
I'm wary of using that in high wear areas or where ti can get wet - i.e. in a flooring situation.
Having said that it seems very easy to use and saves a lot of space - decent internal insulation can lose 100mm/4" off the room.

Here is another link to a project in the UK where they used 6mm Spacetherm Plywood on the floors - ply being better for floors.
Here is a quick search for spacetherm that I carried out on their website.

I haven't looked at all the links yet.
No direct experience of this.


ONQ

 [broken link removed]

 All advice on AAM is remote from the situation and cannot be relied                  upon                                   as a defence or    support  -     in     and      of     itself  -         should          legal             action      be             taken.
 Competent legal and building professionals should be asked to advise in                                                    Real Life with rights    to         inspect     and      issue         reports    on     the                matters        at           hand.


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## JohnJay (24 Sep 2016)

digging up an old thread.....

I will have a similar job to do on a house that I have not yet got the keys for. My engineer/surveyor suggested lifting the floors and replacing with fill/insulation/concrete, but I dont know if my budget will stretch that far. I'll be discarding the old floorboards anyway, so I am thinking of 100/120mm insulation between the joists, membrane, a layer of plywood on top and then finishing with new wood floors/tiling. 

We didnt lift any floorboards during the survey, but the floors feel in good shape and there is no rising damp in the walls. I'm guessing there is a decent void under the floors as there are 2 steps up to the front door, so they will take a fair bit of filling if I am going down that route and I think maybe concrete would be over-kill??


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## Leo (3 Nov 2016)

JohnJay said:


> I'll be discarding the old floorboards anyway, so I am thinking of 100/120mm insulation between the joists, membrane, a layer of plywood on top and then finishing with new wood floors/tiling.



That's all [broken link removed].


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## shweeney (3 Nov 2016)

definitely do it before you move in, I regret that we didn't as the house is draughty and there's a huge void under the ground floor.  I'd imagine insulating between the joists would be cheaper than backfilling the whole thing with concrete, just make sure you seal around the edges of the floor or you'll get draughts.


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## JohnJay (3 Nov 2016)

shweeney said:


> definitely do it before you move in, I regret that we didn't as the house is draughty and there's a huge void under the ground floor.  I'd imagine insulating between the joists would be cheaper than backfilling the whole thing with concrete, just make sure you seal around the edges of the floor or you'll get draughts.



Yeah, I have insulated everything except for the floor in my current house, but I can still feel the wind howling through the floorboards during the winter nights. from what I can see, there is a decent void under the house that would take a lot of filling if I was to do it with concrete. Ive also read that it can be a bit dangerous to fill the void with concrete in older houses as the weight of the wet concrete and fill can cause the bases of the walls to burst outwards. The insulation and plywood might be a safer option!


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## shweeney (4 Nov 2016)

JohnJay said:


> Yeah, I have insulated everything except for the floor in my current house, but I can still feel the wind howling through the floorboards during the winter nights. from what I can see, there is a decent void under the house that would take a lot of filling if I was to do it with concrete. Ive also read that it can be a bit dangerous to fill the void with concrete in older houses as the weight of the wet concrete and fill can cause the bases of the walls to burst outwards. The insulation and plywood might be a safer option!



yeah, there's almost 5 feet of space below our ground floor (_almost_ enough for a basement, but not quite).  One of our neighbours backfilled with concrete but that was as part of a total refurb.  There are videos on YouTube of people insulating under the floor - you can put attic insulation or Kingspan type boards between the joists but you have to leave the airflow to the void intact (i.e you can't just fill the void with beads or foam).  if you have enough space to get under the floor you can do it by just lifting a few boards for access, dirty job though.  I assume you could also put some sort of insulating underlay over the boards and then a carpet or floating wooden floor.  We have stripped boards with no carpet, so the problem isn't just loss of heat, but also draughts from around the skirting and between the boards, should have thought of that when we decided to leave the boards visible.


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## David_Dublin (14 Feb 2017)

We'd been planning to take up suspended floors, like option 1 in OP. Possibly using rigid insulation and sealing gaps as part of a refurb where we plan to improve insulation. I have done the attic, we'd plan to insulate the external walls on the inside, airtight tape at all joints.

Re the suspended floors, now thinking about either:

1) cutting back the joists to the wall and backfilling, levelling with concrete/screed

2) taking up the boards, laying some sort of ply sheet, seal all gaps & to the wall with airtight tape to form airtight layer

Then laying good quality laminate.

We're not interested in underfloor heating. Option 2 obviously only provides airtightness rather than insulation. Is that something we should consider? Heat rises, is there a significant benefit to insulating the floor? The wind whistles through now, so airtight would be a dramatic improvement.


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