Hemp Insulation

Tester46

I am planning to use mats of hemp insulation on the inside of all the external walls in my renovation of an old farmhouse. The reason is it is (a) breathable (b) efficient and (c) "green" i.e. a natural material.

The walls of the farmhouse are stone and rubble with lime plaster - about 18" to 24" deep. From the outside in, the walls will be:

1. limewash
2. lime render
3. stone and rubble wall (with lime mortar)
4. 100mm hemp mats between wooden battens fixed directly to the wall
5. breathable vapour control barrier (intello plus)
6. gypsum plasterboard (not foil backed)
7. skimcoat of gypsum plaster
8. breathable interior paint.

Anyone see any problems with that?

sydthebeat

Tester46 wrote: »

I am planning to use mats of hemp insulation on the inside of all the external walls in my renovation of an old farmhouse. The reason is it is (a) breathable (b) efficient and (c) "green" i.e. a natural material.

The walls of the farmhouse are stone and rubble with lime plaster - about 18" to 24" deep. From the outside in, the walls will be:

1. limewash
2. lime render
3. stone and rubble wall (with lime mortar)
4. 100mm hemp mats between wooden battens fixed directly to the wall
5. breathable vapour control barrier (intello plus)
6. gypsum plasterboard (not foil backed)
7. skimcoat of gypsum plaster
8. breathable interior paint.

Anyone see any problems with that?

IMO the breather membrane should be between the insulation and the stone wall....

have you priced hemp yet?? it tends to be very expensive.
Personally i would slab internally with a board such as fermacell than gypsum plasterboard... it breathes better and allows moisture diffusion better.... they are structurally stronger for hanging onto

RKQ

I have renovated an old barn. I used proclima.
I suggest you incorporate a air cavity - 25mm - between the stone rubble walls and any new dry lining. Breathable construction is incredibly important.

Draught -proofing the junction of the wallplate and top of dry-lining will be very important.

No6

Your insulation is bridged by the timber studs and so is a lot less effective, you would be far better off with a composite slab type drylining system, Kingspan, Extratherm, perhaps not quite as green in manufacture but overall much better perfomance for less thinkness and therefore will save more energy in the long run!! I live in a 90 year old farmhouse drylined with kingspan thermal board and its excellent.:D

sydthebeat

No6 wrote: »

Your insulation is bridged by the timber studs and so is a lot less effective, you would be far better off with a composite slab type drylining system, Kingspan, Extratherm, perhaps not quite as green in manufacture but overall much better perfomance for less thinkness and therefore will save more energy in the long run!! I live in a 90 year old farmhouse drylined with kingspan thermal board and its excellent.:D

personally i would have to favour a designed breathable construction such as the OPs over a non-breathable one, especially on a renovation... buts that my own personal view.

id sacrifice the loss of (theoretical) performance over health risk reduction.

Tester46

sydthebeat wrote: »

personally i would have to favour a designed breathable construction such as the OPs over a non-breathable one, especially on a renovation... buts that my own personal view.

id sacrifice the loss of (theoretical) performance over health risk reduction.

Agreed - that's the main reason we are going with hemp in the first place.

The supplier suggested we put the hemp directly against the wall and put the vapour barrier between it and the plasterboard - why do you suggest putting the vapour barrier between the hemp and the wall? Just curious.

Do you also think we should put a 25mm air gap between the wall and the hemp insulation? How would we manage that? Is the fact that the insulation is bridged by the timber battens really that much of an issue?

Finally, what do you think about the alternatives to gypsum plasterboard mentioned above?

Sorry for all the questions, but you seem to know what you are talking about!

No6

sydthebeat wrote: »

personally i would have to favour a designed breathable construction such as the OPs over a non-breathable one, especially on a renovation... buts that my own personal view.

id sacrifice the loss of (theoretical) performance over health risk reduction.

also theoretical!! the performance is quantifiable though, to op's construction is essentially a construction identical to a timber frame wall or a sloped roof. If he's got loads of room and is prepared to loose 100 to 150mm on all his external walls then he's fine, if the rooms are relatively small he should consider the space loss involved and look at the less green option / options!!

sydthebeat

Tester46 wrote: »

Agreed - that's the main reason we are going with hemp in the first place.

The supplier suggested we put the hemp directly against the wall and put the vapour barrier between it and the plasterboard - why do you suggest putting the vapour barrier between the hemp and the wall? Just curious.

Do you also think we should put a 25mm air gap between the wall and the hemp insulation? How would we manage that? Is the fact that the insulation is bridged by the timber battens really that much of an issue?

Finally, what do you think about the alternatives to gypsum plasterboard mentioned above?

Sorry for all the questions, but you seem to know what you are talking about!

the reason i would suggest the breather membrane between the insulation and wall would be:
1. ensuring the insulation is kept dry by restricting and moisture diffusion from external to internal.. which will happen in days when external humidity is greater than internal. Wet insulation is useless.
2. it will also ensure the insulation is dry by allowing condensation that will form on the cold face of the insulation to disperse into the wall and thus keeping it off the hemp.
3. it will also act as a barrier for any slight gaps any where in the construction that may allow moisture ingress.

i would be interested in hearing the resons to the supplier would have for putting it between the hemp and the plasterboard.....

sydthebeat

No6 wrote: »

also theoretical!! the performance is quantifiable though, to op's construction is essentially a construction identical to a timber frame wall or a sloped roof. If he's got loads of room and is prepared to loose 100 to 150mm on all his external walls then he's fine, if the rooms are relatively small he should consider the space loss involved and look at the less green option / options!!

fair enough

although the OP will avail of further 'quantifiable performances' such as increased thermal mass, preferential decrement delay and the basic comfort of a breathable wall versus a non breathable. He also (theoreticaly) does not need designed background ventilation.... (but im not going to say that!;))

It differs from a trad timber frame or sloped roof because the physical properties of the existing walls are utilised better.

RKQ

Saving energy is the best "green" option. What material thickness is required for each material to reach the same u-value?

25mm air gap prevents the growth of mould - ignore this at your peril.
Talk to anyone experienced with dry rot treatment or lime mortar.

IMO stone has no real insulation value, so incorporate a drylining system that is independent of the stone wall is best. (You may also notice that your stone walls are unlikely to be perfectly plumb)

Tester46

[quote=sydthebeat; i would be interested in hearing the resons to the supplier would have for putting it between the hemp and the plasterboard.....[/quote]

He didn't say, he just suggested putting them in that order (and, to be fair, he was a very helpful engineer from the supplier company who seemed to know the products he was selling). What you say makes more sense though.

I'd prefer not to have to leave a 25mm air gap as well as losing 100mm for the hemp insulation (this is the thickness I need to get to modern building insulation standards apparently). It the 25mm air gap really very important? If it is, how do I create the gap between the wall and the hemp mats?

My understanding of the old stone construction is that it is a bugger (to use the technical term:)) to get it warm, but when it is warm, it stays warm (so long as the heat is on at some level). The insulation is really just to minimise heat loss from the rooms into that old stone wall, but I fully appreciate this is never going to be insulated to modern standards in real terms. The house has to breathe and will be "draughty" anyway - each room will be ventilated through natural draughts in the sash windows and the chimney place anyway, although we hope to keep these to a minimum level required to keep the air fresh.

Builderfromhell

I would suggest the following;
100x 44 studs to help get plumb wall internally.
Also these studs may support new floor or roof if reinforced concrete foundations are included.
I would then use 100mm rockwool which apparently helps regulate humidity of air.
I would fit Xtratherm or Kingspan insulated plasterboard.

The next thing is vapour barriers. Some people would suggest no vapour barrier and allow vapour to breath through stone walls. This I am frankly not sure about.

sydthebeat

RKQ wrote: »

Saving energy is the best "green" option. What material thickness is required for each material to reach the same u-value?

25mm air gap prevents the growth of mould - ignore this at your peril.
Talk to anyone experienced with dry rot treatment or lime mortar.

IMO stone has no real insulation value, so incorporate a drylining system that is independent of the stone wall is best. (You may also notice that your stone walls are unlikely to be perfectly plumb)

a u value is only one element in detemining construction performance and energy conservation. Hemp is carbon neutral / negative..... PU or PIR certainly isnt. hemp is a natural material.. PU and PIR are by products of petrochemical process....

as this construction is breathable, the whole point is to reduce the risk of mould growth.... when foilbacked PU and PIR is used with a polythene vapour barrier in a renovation, the risks of mould growth increase significantly. Condensation cannot escape... weep holes cannot drain moisture away..

with breathable construction this does not happen.

No6

Like everything its a balancing act, performance, budget, space, eco friendly, health..

Stone walls are tricky especially as its difficult to get fixings for the thermal boards, so the framed system may be more suitable. Are you sure its lime mortar tester I've got (very breathable ahem) mud mortar in my stone walls, lime content is zero!! I wonder what R value mud has RKQ!!!:D

RKQ

sydthebeat wrote: »

a u value is only one element in detemining construction performance and energy conservation. Hemp is carbon neutral / negative..... PU or PIR certainly isnt. hemp is a natural material.. PU and PIR are by products of petrochemical process....

I am familiar with Construction Technology. The thickness of hemp to match the thickness of PIR is considerable. I have had this argument, when the inventor of proclima when he visited my home.

sydthebeat wrote: »

as this construction is breathable, the whole point is to reduce the risk of mould growth.... when foilbacked PU and PIR is used with a polythene vapour barrier in a renovation, the risks of mould growth increase significantly. Condensation cannot escape... weep holes cannot drain moisture away..

with breathable construction this does not happen.

Solid Stone walls get wet in severe wind driven rain - water appears internally! The solid stone rubble and lime IS damp for a few months a year. Wet hemp isn't great!
Breathable construction is not much use on a wet wall, during a damp winter.
The OP can PM for a name of an expert on Lime construction.

My advice is from personal experience, not text books. I live with the results. Feel free to ignore my advice, its free.

noel farrell

on a liter note what if the hippies hear and want to smoke it

Tester46

RKQ wrote: »

I am familiar with Construction Technology. The thickness of hemp to match the thickness of PIR is considerable. I have had this argument, when the inventor of proclima when he visited my home.

Yes, but I am ok with having 100mm of hemp insulation, even though I could probably cut that to 25mm with a modern (non-breathable) foil-backed insulation. Do I really need a 25mm air-gap between the hemp insulation and the wall as well? How would I construct that gap?

RKQ wrote: »

Solid Stone walls get wet in severe wind driven rain - water appears internally! The solid stone rubble and lime IS damp for a few months a year. Wet hemp isn't great!
Breathable construction is not much use on a wet wall, during a damp winter.

I'm no expert on this, but there seem to be two main views:
VIEW 1 is to keep it breatheable as this was the way the original stone walls were constructed and meant to be. That means not having the efficiency of a modern build, but accepting this is an old house and working with that.
VIEW 2 is to leave the stone walls as they are, but create a well insulated, non-breathable space inside the stone walls. In other words, build a modern room within the original stone walls.

Both views have their pros and cons. I have gone for View 1 i.e. breathable and am looking for advice on how to achieve that. I think with new lime rendering on the outside and the fact is is a relatively sheletered site, I shouldn't have rain passing right into the house. But someone mentioned a 25mm air gap on the insideof the stone walls to stop the hemp getting wet and mouldy. Tell me more about that...

sydthebeat

tester..
the walls will probably be all over the place so you will probably have a 25mm gap in effect anyway...

the hemp wont get wet and mouldy if you locate the breather membrane between the hemp and the wall, as suggested.

to RKQ, the wall will get wet whatever the internal construction...
the ops suggested construction helps them dry out to a much greater degree that a PIR and vapour barrier construction ever would...

as the ops has stated theres two views on this.. i would be in agreement with the op and err on the side of caution and allow the walls do what they originally were supposed to do.... even with the loss of calculated performance.
but as ive stated above the op would get other performance gains not possible with a PU or PIR type dryline...

RKQ

The 25mm air gap will allow the stone to breathe, as it will be vented at the wallplate due to the traditional roof construction.

I would suggest at least 100mm PIR not 25mm.

The Proclima vapour barrier closes tight in winter but the pores open in the summer heat - in the roof, allowing any trapped moisture back into the dwelling. This natural automatic process is quite clever. Plastic vp does not have the same characteristics.

IMO it isn't a good idea to fix anything to a stone wall. Conside a hemp timber frame construction.

The stone detail is important but the OP may find airtightness around existings truss and purlins is quite difficult - yet these areas will provide the greatest benefit if sealed correctly.

25mm or one inch is really worth considering. If I'm wrong the OP has lost an inch of room. If I'm right the OP has saved his future internal structure from decay.

A external traditional lime render will benefit the structure.

Builderfromhell

Very interesting and informative thread.

It is perhaps worth considering that the hemp may sag over time if not supported. Especially if timber studs are out from wall. You may need to fit battens or use hooks to hold it in place.
I have renovated houses and found insulation had fallen off stud (knee) walls in dormers.

sydthebeat

Builderfromhell wrote: »

Very interesting and informative thread.

It is perhaps worth considering that the hemp may sag over time if not supported. Especially if timber studs are out from wall. You may need to fit battens or use hooks to hold it in place.
I have renovated houses and found insulation had fallen off stud (knee) walls in dormers.

i would envisage the Hemp would be in the form of rigid batts rather then a quilted material.... as in:
http://www.eviee.co.uk/NBT-Natural-Hemp-Insulation.htm

Builderfromhell

Thanks for that Sydbeat, that's a handy site.

gears

Just my 2c worth.
To achieve a 25mm air gap fix 25mm X 50mm battons to wall with spacers/packers at points on the wall where fixing these vertically will leave gaps between the back of the battons and the wall.
Then attach a breathable membrane over these battons preferably with 2 sided tape rather than staples, prevents extra holes in membrane.
Construct a 100mm X 50mm stud wall over the membrane.
Insulate this cavity with the hemp insulation.
Slab over with Fermacell or Sasmox which doesnt need to be plastered over at all just jointed.
Then paint over with a natural paint like Auro.
It's probably more than the OP wants but a 50mm air gap would be easier to construct as 50mm X 50mm could be made into a "timber frame wall" on the flat and just errected and then attached to the wall.

gears

Bit of a late addition here but is what has been proposed even a good idea, I mean vapour barrier on the cold side of insulation is this not just a complete no no...

Tester46

gears wrote: »

Bit of a late addition here but is what has been proposed even a good idea, I mean vapour barrier on the cold side of insulation is this not just a complete no no...

Gears, that's what I thought as well??? But the setup described above does sound very good, (with a 25mm gap).

Tester46

sydthebeat wrote: »

i would envisage the Hemp would be in the form of rigid batts rather then a quilted material.... as in:
http://www.eviee.co.uk/NBT-Natural-Hemp-Insulation.htm

Thanks for that - those mats of hemp are what I am proposing to get - 100mm thick. I am assuming 100mm thick is enough - can't really aford more than that. At the moment I am looking at 25mm gap, 100mm hemp insulation and 10-15mm plasterboard/otherboard. That's nearly 150mm taken off each wall in the room, making my rooms much smaller.

sydthebeat

gears wrote: »

Bit of a late addition here but is what has been proposed even a good idea, I mean vapour barrier on the cold side of insulation is this not just a complete no no...

any reference i make above to a 'breather membrane' is exactly that.... a breathable material whichis diffusion open and has a low vapour sealing effect.

a vapour barrier does not breathe and, correctly, should be located on the warm face of insulation...

however, hemp insulation needs a diffusion open construction so is directly opposed to construction with vapour barriers....

intello plus is a strange on as it can act as both a vapour check and a breather membrane..

it would not be my first choice in this instance,... a solitex membrane would....

Tester46

sydthebeat wrote: »

intello plus is a strange on as it can act as both a vapour check and a breather membrane..

it would not be my first choice in this instance,... a solitex membrane would....

Noted - thanks.

sydthebeat

Jusrt another quick note about foilbacked insulation in renovation projects.

The foil back has been noted to have reducing effects on mobile signals, wifi connections etc.

greenboy

Sounds like a good construction to me...the combination of Hemp and INTELLO PLUS would compliment each other. you would achieve high thermal values, minimal risk of condensation and if moisture ever did get in there it can dry out with the INTELLO inside....its a no brainer to me! I would suggest insulating the 25 mm serivce duct with hemp...maybe get a 40mm mat and split it in half..I think thermo hemp is easy to work with in this way...and then finish with the SASMOX...

RKQ

greenboy wrote: »

Sounds like a good construction to me.......its a no brainer to me! I would suggest insulating the 25 mm serivce duct with hemp...

Seems you may have missed the point of the 25mm gap. Stone and lime walls don't act like conc blocks! Lime breathes and can allow water penetraion.
What stops wind penetration? - even timber frame has breather felt on ply!

Its a no brainer to me!