July 10, 2015

Unvented Foam-Free Roof Retrofit With Dolphin Insulation

IMG_6806There’s a growing demand for high performance roof retrofits. For many homes it can be most practical and economical to improve the airtightness and insulation from the interior. Often the homeowners also don’t want to leave their homes during the retrofit work. That takes spray foam off the table, since chemical exposure to spray foam during installation is a serious health risk. (Those haz-mat suits and gas masks aren’t just for show).

Dolphin Insulation, a cellulose insulation contractor based in Littleton MA, offers interior roof retrofits that are both high performance and foam-free. Over the years they’e refined their approach, and now provide unvented roof retrofits that exceed code requirements for insulation and vapor control. They do this using dense-pack cellulose along with Intello Plus airtight, smart vapor retarding membrane.

Beyond Roof Weatherization

Dolphin is pushing the industry far beyond conventional weatherization and into Deep Energy Retrofit levels of performance. By using cellulose insulation, they also complete the work without danger to themselves or the building occupants – and with minimal inconvenience – so life can go on largely without disruption in the living areas below.

These days Dolphin takes on a lot of “hot roof” retrofit projects that aim for minimum R-40 insulation. By including the attic in the conditioned space, it becomes useful for storage and HVAC. For HVAC systems in particular it’s a win-win scenario. The airtight and super-insulated enclosure makes an HVAC system more efficient, but also reduces heating and cooling demand so the homeowner can save money on a downsized system. David Posluszny, Dolphin’s Energy Engineer (recently featured in Home Energy Magazine’s “Thirty under 30“), notes: “We worked to an R-40 because [the owner] was having an air conditioner installed in the attic.  However, the house has existing baseboards for heating.  If the HVAC was going to be a furnace in the attic we prefer going to an R-60.”

IMG_7594They start by furring inward from the 2×6 rafters with 2x4s to create a thermally broken “double roof”.  They also fur in the gable end walls. Then they install Intello Plus by stapling to the inside of the studs. They tape horizontal and vertical seams with Tescon Vana 75 (3″) or Vana 100 (4″) solid acrylic tape for robust airtight connections. Whenever possible they use double-wide (~10′) Intello Plus to keep horizontal connections down to a minimum. For this project they used 10′ wide membrane over the gable and 5′ wide membrane for the remaining areas on each side down to the eaves.

They follow with  vertical plywood strapping over the rafters and studs. This strapping ensures that they avoid staple tear-outs when dense-packing to levels above the industry standard 3.5 pounds per cubic foot. For maximum strength they also position vertical taped seams to coincide with strapping. (Note from 475: we typically recommend horizontal strapping perpendicular to studs/rafters. But in cases where higher density is desired, vertical strapping can help prevent staple blow-outs.)

Beyond Typical Dense-packing

IMG_6811Once the strapping is in place, they like to dense-pack to as much as 4.5 pounds per cubic foot. At this density, the Intello feels quite hard (for comparison, at 3.5 psf the density is often likened to a “firm mattress”). David notes: “It is a great product. Our crews like using it because of the strength.  Dolphin Insulation packs cellulose to 4.5 pounds per cubic foot. We have tried several products on the market to contain this density, but all seemed to pull out, give way, or stretch too much. The Intello Plus stands up to the pressures.”

After several projects, Dolphin has optimized their dense-packing approach. They prefer to allow the bays to “communicate” and pre-fill all of them.  Then they go back and dense-pack one at a time.  The pre-filling in the adjoining bays serves the function of separating the bays.  David: “With our machines (extremely powerful and expensive) we find the best results with this method.”

They cut one opening in each bay for blowing in. After the bays are packed, they patch the blow holes with 6″ squares cut from Tescon Vana 150. David adds: “Of course there are plenty of spots thicker where the Intello Plus bulges out a bit with the massive cellulose.  Those areas have higher R-values, but we don’t count those [in the R-40 total].”

IMG_6805With Intello Plus, Dolphin achieves high performance insulation, airtightness and smart vapor control in essentially one step.

Dolphin also makes improvements at the wall connections. They extend Intello Plus all the way to the wall airtight layer with resilient stapled and taped airtight connections. In practice, it’s challenging to get those connections perfect. By dense-packing into the attic joist bays – a physically demanding job (see photo) – they balance the air and vapor control benefits of both Intello Plus and hygroscopic cellulose at that important transition.

Vapor Variability = Venting Not Required

The Dolphin team notes “there is no venting in the assembly, and we don’t need any thanks to the Intello Plus.” 475 High Performance Building Supply’s best practice recommendation is to vent cathedral roof assemblies. But there are times when roof venting is either impossible or impractical (ie the house has a new roof). In such cases, Intello Plus provides the robust airtightness and vapor control needed to keep moisture levels safe, because of its best-in-the-industry vapor variable properties. This has been documented in our project spotlight on the recent Middlesex VT Passive House, which takes full advantage of Intello Plus for its unvented, foam-free and super-insulated flat roof. In combination with Tescon Vana tape, with 100 year age-tested performance, this resilient system can be expected to far outlast any foam-based solutions while providing more reliable and predictable air and vapor control.

Most building codes or inspectors do not fully understand the safety that smart vapor control can bring. The route to choose in those cases is to work with the 475 technical team and convince the inspectors that:

  1. Intello airtightness verified with a blowerdoor test is equal to or better than foam inboard of the sheathing – and certainly more durable.
  2. Intello’s vapor variable properties allow inward drying of unforeseen moisture (caused by rain, construction moisture, or new air leaks from occupants’ puncture holes). With Intello these can dry out in summer – something that is not possible with foam. By request, we can provide a worst case WUFI Pro study for your location to press the point.

For best practice interior roof retrofits, we like to advocate a hybrid approach that combines Intello Plus at the interior with back-venting at the exterior. This can be done with or without a new roof, but we acknowledge it does take more effort. With Intello at the interior, in most cases the back-venting is not required.

Further Discussion

For a detailed discussion of retrofit approaches, see our blog post Foam-Free DER: Roof Assemblies, get our free downloadable CAD details here, and take a look at Alex Wilson’s interior roof retrofit case study: Can’t vent at valleys and dormers? Use a smart vapor retarder (not foam).


We can dramatically reduce residential energy use and help solve the climate crisis – with retrofits like this one multiplied by 10 million across America





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13 Responses to Unvented Foam-Free Roof Retrofit With Dolphin Insulation

  1. Katy Hollbacher July 14, 2015 at 12:52 pm #

    I love the idea of not venting a roof assembly that’s insulated only with dense-pack cellulose since otherwise it’s all but impossible to go foam-free if you can’t insulate above the roof deck. But even with the best-quality installation and blower door for airtightness verification, this approach doesn’t meet code and would make me nervous in most climates. I’m really interested in hearing the track record with this in various climates (5+ years installed) as well as details on your odds of success in getting inspectors’ signoffs. Thanks for an inspiring post!

  2. Ken July 14, 2015 at 2:04 pm #

    Hi Katy,
    Thanks for your great comment. We’d ask, what if you have foam insulation but not airgithness? Then the foam is meeting the “letter of the law” but not the intent of it. We would especially be worried about maintaining airtightness by depending on the foam insulation, as even if the thing itself is airtight, it regularly fails in the connections. On the other hand dense-pack insulation and an inboard airbarrier (that is vapor intelligent no less) as an integrated assembly provides far more robust protection against moisture damages and meets the intent of the code. We have had local code officials regularly agree with this assessment and approved its use. INTELLO is a proven product. We look forward to showing more examples. Cheers.

  3. Scott S July 14, 2015 at 3:35 pm #

    Does properly installed Intello mitigate the vapor concerns noted from Building Science Corporation BSI-043 with regard to unvented cathedral ceilings?


    What about exterior vapor intrusion? For a dense pack cathedral ceiling roof assembly, if the roof sheathing gets damp is it reasonable for the sheathing to dry to the exterior (through roofing paper and shingles) or to the interior (through 6″-8″ or more dense pack cellulose + Intello). For new construction I would think taping the roof sheathing with Tescon Vana to limit air movement through the sheathing would be strongly encouraged?

    • Floris July 14, 2015 at 5:07 pm #

      Scott there are multiple reasons that a flatroof with INTELLO Plus on the inside does not lead to the same issues and concerns that BSC pointed out in their “don’t be dense” report:
      – You can verify the ceiling is densepacked behind the translucent INTELLO Plus, both by feeling (firm mattress), by counting bags (separating cavities) and spot density testing.
      – Not blowing in from outside on a flatroof helps too
      – Not counting an painted sheetrock as your vapor retarder (class III at best) and airbarrier. A flatroof can only dry in, so needs a INTELLO a smart vapor retarder
      – Asphalt shingles are vapor closed as well – so cathedral ceilings that are unvented need to have the same ProClima vapor variable retarder on the interior

      Vapor closed roofs (flat or asphalt singles), should not have so much issue with exterior vapor intrusion, as those roofs are vapor closed. It would be good to tape the roof sheathing with TESCON VANA – to limit air movement/windwashing of the insulation in all cases.
      The only shingles that result in vapor intrusion from outside – are cedar roof shingles – when they are wet, solar driven diffusion could drive vapor inward. Hence they should be vented. This is required by code and also our best practice solution for a long lasting cedar roof. THe shingles will dry faster and no humidity will be driven inward as it is vented away.

      So, yes – INTELLO does mitigate the vapor concerns as noted in the BSI-043 report (with some exceptions, like thick green roofs with PV over them (ie super heavily shaded) – or ones where damp insulation was installed.

      And Chuck, thank you for expressing your support for this approach as a valid ‘air-impermeable insulation’ per R806.5 – 5.1 unvented attic/rafter enclosures

  4. Chuck Miller July 14, 2015 at 3:45 pm #

    As with any system the key is in the details and in having a mechanic that can and will make sure details are followed. There are risks in all aspects of the building world, no guaranties. However, thanks to our government and the smart building program lots of money has been invested in testing different systems. See Building Science Corp for good information. I believe if you can get your mind around the fact that 99% of moisture moves on air not by diffusion then this approach makes perfect sense and is practical. I am old school and believe in back venting and then dense packing just in case, but studies to date that I’ve read claim that even a ridge vent without soffit vents and proper vents can help relieve moisture do to the capacity of the cellulose help moisture migrate. Let’s look at this from another angle, we’ve been dense packing exterior walls for years with good success and a roof system is simply a wall set at a slope. I am a building official in MA and would not have an issue supporting the approach as stated and complete as shown.

  5. Katy Hollbacher July 22, 2015 at 6:21 pm #

    Thanks, everyone, for great insights. I would still like to know the coldest climate anyone has used this approach with success?

    I would be game to try it on the right project, but the one lingering concern I would have is that you can’t guarantee what will happen to that beautiful airtight assembly after a new owner takes over.

  6. Bruce Friedman July 28, 2015 at 5:59 pm #

    I really like this approach. I did briefly talk to the engineer at Dolphin for one of several projects I have going on in their local area but at the present they are booked thru the late fall. Good for them.

    Ken – what would you recommend for a 2×10 shed roof with typical asphalt shingles. The interior board has been removed and we will be replacing the roofing as well though it will be difficult to vent this low pitch roof. I would like to use dense pack but there are some that need to be convinced this is a good approach vs CCspf/ OCspf combo insulation (2″ CC + the remaining OC)

    Thanks in advance for your help.

    Regards – Bruce

    • Ken July 29, 2015 at 9:21 am #

      Thank you for your comment and question. The dense pack with inboard INTELLO airtightness and vapor control is robust. We suggest this approach for unvented vapor closed flat roofs as well (given the “rules” are followed) see that blog post here: http://foursevenfive.com/the-ten-golden-rules-for-foam-free-flat-roofs/ Happy to discuss. – Ken

  7. Dennis August 26, 2015 at 1:45 pm #

    Dolphin Insulation is the best at what they do! The only ones that know how to create the perfect indoor climate throughout these crazy New England seasons! I have tried multiple things including a new roof and adding ventilation, nothing helped until David from Dolphin came by and wrote up a solution based plan for my home. They got rid of all my ice dam issues using this approach and I live in Maine.

    • John August 26, 2015 at 5:27 pm #

      That’s fantastic to hear, Dennis. Thanks for mentioning it. We love hearing feedback after the project is done.

  8. daniel December 1, 2015 at 2:57 am #

    really useful in saving energy bills for home .thanks for posting.

  9. daniel December 7, 2015 at 1:54 am #

    nice insulation method .thanks for posting


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