Another Airtightness Q

creedp

I know this has been asked before but I'm at the stage now and a decision is required. I have concrete slabs on 1st floor and despite that I requesting my builder wrap the slabs in solitex (and despite him agreeing to it) he didn't do it. I wasn't on site for the job and afterwards he simply shrugged his shoulders and said he doesn't wrap slabs!

Therefore, I would like to ask what is best to do now to minimise air leakage around perimeter walls. I was contemplating using airtightness tape to tape slabs to perimeter upstairs or would it be better/easier to tape insulation to perimeter walls? Of course there is his view that there is no need to do this as the perimeter insulation will be held tightly against wall by screed do no possibility of airleakage. In any case he thinks I'm mad as the cavity is pumped so no air circulation in cavity.

Also is there any need for airtightness measures on ground floor? Is is overkill to be considering taping ground floor insulation to perimeter wall? I have quinnlite blocks on first 2 courses and builder didn't plaster down to slab - he didn't plaster the last course - as he said this would create a cold bridge. Does this lack of plaster on last course make the airtightness problem worse?

Thanks

Radonman

First thing first, your builder sound like a complete ass!!! anyhows, the fact that he did not wrap the slab is not a disaster you can still seal the slab but its more expensive time wise and material wise (trust me we have done it several times) - what you need to do is seal the joints where the slabs meet, preferably before you install the suspended ceilings with either an air sealing tape (you would need to prime the slab first) or with strips of Solitex (your choice) sealed to slab with sealant. All services through the slab also needs to be sealed around. Where the slabs sit on the internal leaf of the cavity wall we have found that the easiest method is to clean all debris from the joint and pump it with sealant.
These methods do work as we have had several houses tested.
On sealing the block to the floor I would especially as its not plastered but it does depend on what rating your looking for - hope this helps

creedp

Thank Radonman. I know it is something that has really bugged me from early on on the build and everytime an airtight issue comes up I am reminded of it! Im afraid its too late for the underside of the slab as although I taped the slab to the perimeter wall I didn't consider the necessity to seal the joints between the slabs. Ah well!

Al I can do now is deal with what's left - are you advising that I should seal both the ground floor and first floor to the perimeter wall and would priming the wall and floor and taping be the best option? What kind of tape would be best, e.g. the 'green' siga tape. I understand there is a 150mm siga tape with split backing tape which might be convenient for installing in this location. Would it be worth the additional cost over the std 100mm tape?

Thanks for advice. I'll be glad when this build process is over as its been difficult, constantly trying to be one ahead but invariably left behind!! If I ever again build a house - hopefully not - all I would say is that there are horses for course in the building game as well as in every other game and if you select the wrong horse you're on a loser despite all subsequent efforts.

sinnerboy

creedp wrote: »

despite that I requesting my builder wrap the slabs in solitex (and despite him agreeing to it) he didn't do it. I wasn't on site for the job and afterwards he simply shrugged his shoulders and said he doesn't wrap slabs!
Thanks

Every once in awhile I have an issue like this. Usually when the client has "his" builder-never with any of my trusted regulars. Your builder sounds like a dishonest arrogant twerp. He won't change unless you control the purse strings.

You should prime and tape the slabs/wall junction as you say - but you should patch/strip over the slab to slab joints too as the joints as they will allow a bypass route otherwise.

Do you have a contract administrator ? If so , if it was me ( the CA), I would have the contractor do this at his expense. If you don't have a CA - well it's difficult to advise. The contractor may have seen you coming.

creedp

sinnerboy wrote: »

Every once in awhile I have an issue like this. Usually when the client has "his" builder-never with any of my trusted regulars. Your builder sounds like a dishonest arrogant twerp. He won't change unless you control the purse strings.

You should prime and tape the slabs/wall junction as you say - but you should patch/strip over the slab to slab joints too as the joints as they will allow a bypass route otherwise.

Do you have a contract administrator ? If so , if it was me ( the CA), I would have the contractor do this at his expense. If you don't have a CA - well it's difficult to advise. The contractor may have seen you coming.

Thanks Sinnerboy. I think you hit the nail on the head re: last sentence above. These guys know everyhing about building and you know nothing and unless you have a professional on your side Im afraid you're onto a loser. By the way in response to your Q, No I don't have a contract administrator. Originally I was going to go direct labour and hire a CA, even had one lined up and was advised/persuaded to go down the experienced contractor route because I live/work approx 40 miles from site.

Thanks I will go ahead and tape the slab/wall junction. I was just wondering about the slab to slab joints. Currently on the upper side of the slabs the joints have been filled with mortar and I [foolishly] thought that as the slabs were covered with insulation and screed upstairs that this should be sufficient to make them airtight. I am now aware of the problem with the underside of the slabs but unfortunately the suspended ceiling is already installed and slabbed. Will this be very problematic for my airtightness levels? I know I should be trying to get best possible levels and I have taped every opening and used membranes on the ceilings but will this problem mean that I won't be able to achieve a reasonable level for the purposes of efficiently running a MVHR Unit?

Thanks for advise [even if it does depress me:(]

sinnerboy

All is not lost entirely. Think about the routes that your internal heated air will attempt to take. Your plastered ceiling is in place now so it is really your first defense line.

Use intumescent silicone to seal all cable penetrations. Avoid recessed lighting - only tracks if you want spots. Anything larger such as vent ducts / svp / other drain pipes are tricky but again I would cut back plater to allow a min 6mm wide gap to fill with caulking silicone. This has a more chalky feel when set compared to the waterproofing silicone and will harmonise more easily with the skim finish. I would expect your contractor to sneer at this so get a "handyman" in to "snag" if you have to. The AT tape people should be able to help you find someone.


Too late now - but has the 75-100mm strip of external wall in line with ceiling void been plastered or covered by taping ? If so good if not - pity.

creedp

sinnerboy wrote: »

All is not lost entirely. Think about the routes that your internal heated air will attempt to take. Your plastered ceiling is in place now so it is really your first defense line.

Use intumescent silicone to seal all cable penetrations. Avoid recessed lighting - only tracks if you want spots. Anything larger such as vent ducts / svp / other drain pipes are tricky but again I would cut back plater to allow a min 6mm wide gap to fill with caulking silicone. This has a more chalky feel when set compared to the waterproofing silicone and will harmonise more easily with the skim finish. I would expect your contractor to sneer at this so get a "handyman" in to "snag" if you have to. The AT tape people should be able to help you find someone.


Too late now - but has the 75-100mm strip of external wall in line with ceiling void been plastered or covered by taping ? If so good if not - pity.

Sinnerboy, Im going to risk annoying you further by continuing with this thread:). I was going to tape around all the penetration to floor and wall with A/T tape rather than using silicone but will consider the chaulking silicone as an alternative.

I'm afraid its a case of being 'a pity' as I asked for this to be done in that I insisted that all external walls be scratched from floor to ceiling and when I called on site one evening I found the timber frame for the suspended ceiling in place without the wall above it plastered. He argued with me that his plasterer wouldn't plaster the area seperately to rest of wall as it could lead to a crack in the plaster at the ceiling line. I know this may all seem crazy to you experienced boys but believe me I have tried and obviously failed miserably:o.

Thanks again

sinnerboy

If the wall area of the ceiling void is not plastered than the wall fabric there remains relatively porous. So your only line of defence is the plasterboard ceiling.
I'm not aware of any tape product which can architecturally seal say a pvc drain pips to a plastered ceiling thus the caulking silicone recommendation.

I would still at the top of slab level tape seal pipe-to-slab.

On a tangential note I find it lamentable that such a contractor has work when so many good guys I know don't.

Radonman

Sinnerboy speaks a lot of sense, plus I can't believe the builder would not put a coat of plaster on your internal wall - I hope your keeping a nice sum back for the last payment!!
Anyhows regarding the Siga tape, personnally I find them very expensive, try Tescon Tape from the Proclima range of tapes for sealing around pipes through the concrete slab although not an ideal product (both the siga and proclima are really for timber) be sure to prime the slab first to help with the seal - you could still do this with the underside of the slab even though the suspended ceiling is in, takes time but is all helps espically if your installing a HRV unit

Radonman

Sorry just read that the slabs are up and plastered now thats a problem unless your going to take the pain and take them down the HRV unit will deff not work to its potential as it will draw air from the outside where ever it can - Sorry

sinnerboy

creepd - one thing to keep front and center of your mind through all this. The completed building and it's quality. Sad to say this will be achieved in spite of rather than because of your "builder". Don't get worn down by transient , if attricious issues raised by him. It's not too late appoint a professional* to look after your concerns even at this stage. ( Build quality and perhaps payments - caution depending on what contractual arrangement you have in place already ) .

A common mis conception is to consider that the builder "knows what he's doing" and therefore no professional is needed. A profesional will ensure that what the builder is required to do is spelt out in clear contractual terms in drawings and specification documents which will include terms relating to quality , compliance with spec and resulting consequences for payments.

Sad to say in your case that the builder "knows what he's doing" :mad: and therefore professional is needed.

*A good Architect , Architectural Technician , Engineer or Surveyor won't cost you so much and will re pay his/her fee. I think you need someone.

.

Radonman

Agreed - Plus takes the pressure of you and puts it back on the builder