HRV / Airtightness

thunderRoad

Hi guys,
not sure if this question has been asked/answered before, also might not be a 'simple' answer,

in a traditional concrete build are HRV systems a waste of time/money, no open fires, and roof/ceiling done with vapour barrier, no drylining?

alot of info i seem to be getting is aimed at timberframe construction hence question...

thanks

sinnerboy

thunderRoad wrote: »

Hi guys,

in a traditional concrete build are HRV systems a waste of time/money,

thanks

no - air tightness and HRV are very worthwhile

You must achieve a min level of air tightness to comply with b regs

for guidance look here

http://www.environ.ie/en/Publications/DevelopmentandHousing/BuildingStandards/FileDownLoad,18749,en.pdf

http://www.environ.ie/en/Publications/DevelopmentandHousing/BuildingStandards/FileDownLoad,18751,en.pdf

did not understand the rest of your post can you re phrase it please


.

thunderRoad

thanks sinnerboy,

exactly what i was looking for,

up until now the airtghtness info i was gettin was aimed at timberframe construction, thought that you might have to put a vapour barrier over blockwork and beneath plaster to achieve airtightness to form contimious seal,

sorry for the phrasing, not good at putting into words what i mean

thanks again

Slig

The reason it is mostly shown on timber frame is that timber frame is an easier system to super insulate than blockwork. Its also mor "off the shelf" than blockwork so its marketed more.

Retro-Fit

HRV is especially needed for concrete built, each occupant produces 7 lt of water vapour per day. Block walls underperform their design thermal performance, 0.25 when analysed only achieves 0.75 at best when cold bridging and vented cavity issues are considered. Hole in the wall vents and air changes over 5 are extremely wasteful especially with a view to projected energy costs ( though you's almost think energy can only go south these days. When you get to the stage where you realise the benifits of HRV you will have come to appreciate the major deficiencies with cavity wall construction. The massive cold bridge at the rising walls, the one at reveals and thresholds/cills. The problems at eaves and chimneys. Also the terrible thermal capacity of concrete blocks(cant retin heat- phase displacement) and of course the issue of water condensing on the many cold surfaces.

Slig

Retro-Fit wrote: »

HRV is especially needed for concrete built, each occupant produces 7 lt of water vapour per day. Block walls underperform their design thermal performance, 0.25 when analysed only achieves 0.75 at best when cold bridging and vented cavity issues are considered. Hole in the wall vents and air changes over 5 are extremely wasteful especially with a view to projected energy costs ( though you's almost think energy can only go south these days. When you get to the stage where you realise the benifits of HRV you will have come to appreciate the major deficiencies with cavity wall construction. The massive cold bridge at the rising walls, the one at reveals and thresholds/cills. The problems at eaves and chimneys. Also the terrible thermal capacity of concrete blocks(cant retin heat- phase displacement) and of course the issue of water condensing on the many cold surfaces.

I really wish that was the case, unfortunately HRV is still a huge investment for most people (some still cant justify construction drawings) and the associated damp problems associated with super insulation of houses havent been fully appreciated.
The cavity wall is still hanging in there by the skin of ts teeth, its been butchered and modified and upgraded because people still prefer a system that they knew half worked over any one they dont know anything about.

thunderRoad

cheers lads,
think i'll be going with cavity wall,mostly due to cost, as in cheap labour cos dad is a blocklayer
think i'm gonna go with

100mm block (+225mm stone on front)
40mm air
100mm kingspan/similar
150mm quinnlite/similar

I suppose the main thing i was tryin to ask was that ' is a block wall too permeable to allow a hrv to work properly?'

got some really good info from the docs that sinnerboy sent,

Also, I take it that putting a vapour barrier below the joists and above the plasterboard is the way to go?, and any recomendations for makes/models of hrv system?

sinnerboy

thunderRoad wrote: »

and any recomendations for makes/models of hrv system?

http://www.sap-appendixq.org.uk/search.jsp

thunderRoad

thanks again sinnerboy

sinnerboy

give this some serios thought - ask your dad to consider

build 215 inner leaf quinn blocks
80mm pir (kingspan / xtratherm/quinn therm/ballytherm ) - foil faced

BUT .....................

build outer leaf later

---

reasons

it is vital that all boards are

1 built tight against the inner leaf
2 tightly butt jointed - along straight runs and at corners AND FOIL TAPED

leave wall ties sticking out for the outer leaf . before you start to build that you should find yourself looking a fine seamless silver box , with all stepped dpc's present and correct . NB do not use pir boards at the cavity base - pir soaks up water . use extruded , not expanded , polystyrene from cavity base up to dpc level

you will find it much easier to keep a clean cavity this way - all the same leave out every 5th block at the base of your outer leaf to sweep out the odd mortar dropping

this must only be attempted using a 215 inner leaf - for temp struct stability

thunderRoad

just talking it over, sounds like very good idea, gonna give suppliers a shout and check out costs.

thanks a mil

would love to see the big silver box on sunny day, will have to wear shades building outside leaf!:D

sinnerboy

one thing to add - b regs and homebond require that where the overall cavity exceeds 110mm - you must have a qualified insured professional engineer to specify the wall ties ( you should have one appointed in any event so simply draw the cavity width to his/her attention )

you must maintain a 40mm air space so cavity will be 40+80 = 120mm

Slig

sinnerboy wrote: »

one thing to add - b regs and homebond require that where the overall cavity exceeds 110mm - you must have a qualified insured professional engineer to specify the wall ties ( you should have one appointed in any event so simply draw the cavity width to his/her attention )

you must maintain a 40mm air space so cavity will be 40+80 = 120mm

I have just got some prices back, they are very general but I think it will be a help.
150mm lightweight blockwork inner leaf over 100mm standard conc. blockwork inner leaf for a 180sqm, 2 storey semi-d is €3500 extra.
Thats for blockwork alone, so you might be able to save some on the labour.

thunderRoad

sinnerboy,
engineer already specified 150 cavity, so will follow his details on that, thanks

slig,
best quote i got for 150mm lite blocks was 1.88/block incl. vat, havent got quotes back yet for 215mm.

cheers lads

Lazybones

Hello Sinnerboy,

I'm very interested in your cavity wall detail and insulation make up as you outlined to the OP query.

Just so I understand correctly the make up of the construction would be as follows:

215 Inner Quinn Lites
80MM PIR (I presume 100MM PIR could be used also? - depending on budgets of course!)
All joints tightly butted and FOIL Taped
40MM Cavity
100MM Dense Block outer Layer (built later)
In my case I will be having stone facing on the gable ends of the house

I really like the potential that this gives for ensuring attention to detail on the insulation.

Have you actually seen a real life build completed as per this spec and construction method?

What potential U value would this spec of construction achieve?

Where is the air tightness barrier layer put? (is this a layer or material that is attached to the inner leaf ? - please forgive my ignorance if this is a simplistic question.

Are there any other special considerations that need to be kept in mind in dealing with a potential construction thickness of 435mm (215+80+40+100)

Sincere thanks in advance for your helpful input with my queries.

Best regards,

Lazybones

sinnerboy

Lazybones wrote: »

Hello Sinnerboy,

I'm very interested in your cavity wall detail and insulation make up as you outlined to the OP query.

Just so I understand correctly the make up of the construction would be as follows:

215 Inner Quinn Lites
80MM PIR (I presume 100MM PIR could be used also? - depending on budgets of course!)
All joints tightly butted and FOIL Taped
40MM Cavity
100MM Dense Block outer Layer (built later)
In my case I will be having stone facing on the gable ends of the house

I really like the potential that this gives for ensuring attention to detail on the insulation.

Have you actually seen a real life build completed as per this spec and construction method?

What potential U value would this spec of construction achieve?

Where is the air tightness barrier layer put? (is this a layer or material that is attached to the inner leaf ? - please forgive my ignorance if this is a simplistic question.

Are there any other special considerations that need to be kept in mind in dealing with a potential construction thickness of 435mm (215+80+40+100)

Sincere thanks in advance for your helpful input with my queries.

Best regards,

Lazybones

you could also use quinn block for the external leaf to maximize u value

if your engineer will sign off on a 150 cavity ( carefull selection and spacing of ties ) - then you could use 110 pir in cavity

the air tightness barrier in this construction would be WET plaster internally - look carfefully at links i posted earlier - devil is IN THE DETAIL

u value will depend on what permutation you select - ( I will not calculate them all - sorry - ask your products rep for this ) but ball park 0.25 -0.23

Of course i have done this in real life !

Other consideration - footings min 3 x wall thickness - watch out for that

Quazzie

sinnerboy wrote: »

give this some serios thought - ask your dad to consider

build 215 inner leaf quinn blocks
80mm pir (kingspan / xtratherm/quinn therm/ballytherm ) - foil faced

BUT .....................

build outer leaf later

---

reasons

it is vital that all boards are

1 built tight against the inner leaf
2 tightly butt jointed - along straight runs and at corners AND FOIL TAPED

leave wall ties sticking out for the outer leaf . before you start to build that you should find yourself looking a fine seamless silver box , with all stepped dpc's present and correct . NB do not use pir boards at the cavity base - pir soaks up water . use extruded , not expanded , polystyrene from cavity base up to dpc level

you will find it much easier to keep a clean cavity this way - all the same leave out every 5th block at the base of your outer leaf to sweep out the odd mortar dropping

this must only be attempted using a 215 inner leaf - for temp struct stability

Odd. I came up with exactly this construcion method myself about a week ago and even asked Sydthebeat to work it into my spec that he is preparing. To me it makes the best sense, and I think its the way I'm going myself. I found some really interesting information in this pdf that really highlighted the importance of proper installtion of insulation in a cavity wall set up.

hogandrew

I am just about ready to purchase a heat recovery unit and have been quoted 2080 stg for the unit and ducting. Is there better offers to be found. I seen some on ebay. I think i read that the efficency was about 75 to 80% but the budget is type so top of the line is not an option.

I think its 14 valve the system. Anything i should look out for

sinnerboy

if you don't choose a SAP appendix Q unit - a BER assessor MUST apply default efficiency of 66%

read this thread carefully

http://www.boards.ie/vbulletin/showthread.php?t=2055385732&highlight=hrv+fire

hogandrew

sinnerboy wrote: »

if you don't choose a SAP appendix Q unit - a BER assessor MUST apply default efficiency of 66%

read this thread carefully

http://www.boards.ie/vbulletin/showthread.php?t=2055385732&highlight=hrv+fire

Thanks sinnerboy. never would have taught of that