April 16, 2012

How to airseal a (rowhouse) roof

Working from top to bottom we start with the easy part, the roof.  To not have to seal an additional 40+ roof joist (so 80+ joist penetrations into the load bearing party wall) it is recommended to use INTELLO Plus under these joist. This conveniently puts the airtight layer on the inside of these joist and thus saves you a large amount of taping and sealing – and besides saving materials, it also reduces the number of junctions and thus limits the amounts of application errors that will be made. Which should result in a tighter house and better blowerdoor test result.

Most rowhouses have flatroofs or use bitumous or asphalt shingles as roofing, which are vapor closed, so it is important to use an airtight intelligent vapor retarder on the interior of the bulk of your insulation. This protects this insulation in winter from humidity and condensation, while allowing the assembly to dry inward in the summer. Offering you both airtightness, insulation netting (INTELLO Plus is reinforced) and protection against moisture accumulation in the roof structure.

Typically there are few skylights/doors in the roof, so the amount of penetrations to seal should be minimal (especially if you can omit your plumbing vent because you are allowed to use an AAV in your jurisdiction).

Putting the membrane up

Applying the membrane is quite straight forward. Running it perpendicular to the beams is typically the most material efficient way to apply it. See photo below. Running it in this direction will allow you to accurately size the overlap. The recommended minimum 2″ overlap is indicated on the membrane and these guides make running the membrane straight across the joists straight forward. The steps to apply the membrane are explained in the video below and are as follows:

INTELLO install to brownstone roof in progress, seams taped with UNITAPE

  • Measure the length of the roof
  • Cut the membrane about 12″ longer than this measurement
  • Start the membrane on one end, overlap the adjoining wall by at 2-3″ so you will have sufficient material to make an airtight connection to the wall and not run out of material if you had cut the membrane at a slight angle.
  • Mark the first 5 joists app. 56″ from the wall
  • Staple the first corner while lining the membrane edge up with the mark
  • Move over to the joist 5′-6′ into the room. Pull the membrane taut and staple the membrane to it while lining it up with your mark
  • Move to the wall and pull the membrane taut in a triangle formed by the two staples. Staple the membrane close the wall into the joist that is half way in-between the two staples you just set.
  • This method will set up a nice straight run, with the least chance of creases and thus the best airtight result.
  • Start to staple the membrane (staples in the direction of the stud, every 2″) to entire width of the membrane at the first joist.
  • Repeat at every joist and work your way across the room, keeping the membrane nice and taut.
  • Repeat until the entire roof is covered.
  • Tape all seams with TESCON VANA or UNITAPE
Watch video of INTELLO application with the triangle method

INTELLO connection with CONTEGA FC to plaster walls

Now attach the INTELLO Plus to the walls. In case the airtightness of the wall is achieved with the same membrane, a simple tape connection is best. Similairly, if airtight taped plywood or OSB is used in walls, make a tape connection to these elements.

In a brick (historic) rowhouse (or Brownstone) the partywall airtight layer might be made with plaster. In that case use CONTEGA FC felt tape and:

  • Adhere the CONTEGA FC  to INTELLO Membrane
  • Embed the tape into the first layer of plaster (scratch coat)
  • Add a second layer of plaster to get a truly airtight coat of sufficient thickness

    Flatroof with INTELLO Plus membrane connected to interior insulated brick wall

Run counter battens (2x’s) every 20″ that will carry the majority of the weight if blowing in dense-pack cellulose. These will also act as the service cavity in your ceiling for ducts, lights and wiring.

Making your roof airtight is very important and with the Pro Clima system will be easier, lightweight (membrane is much lighter than plywood and OSB) and verifiable.

Allowing a some slack at corners when connecting membranes to different materials allows for slight settling or movement of the building. Guaranteeing air-tightness for the long term.

INTELLO in roof with counterbattens, ready for cellulose insulation

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  1. How to airseal a Brownstone to PH standards (party walls) | Four Seven Five - May 17, 2012

    […] See previous blogpost about sealing a row house roof with INTELLO Plus. […]

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