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Should You Retrofitor Rebuild?

Log construction makes goodeconomic sense in areas where

there are local trees to cut and use.So does making the effort to rescueand rehabilitate our existing logstructures since the cost to erectthem has already been spent.

We call this cost “embodiedenergy.” Embodied energy is all themanufacturing, shipping, and laborto build our homes the first time.

What is Payback?Payback is all the money, work, andfuel that you save if you retrofityour house to become energyefficient.

Chapter 6Retrofit

It is usually true that if you havea log house that isn't rotting into theground, it is probably worth retro-fitting. This is especially true inremote communities of Alaskawhere shipping costs and heatingfuel prices are very high.

Log building restorationprojects may also be for historical oraesthetic reasons and not just forenergy efficiency. Very old buildingsmay need many improvements toextend their life to reach theirpredicted payback time.

Retrofit ChecklistThe following checklist is meant to guide you through the assessment process and to focus

your efforts on areas needing improvement. Details on how to do some of the work follow.

Foundation and Floor Assessment

❏ Is foundation above the flood plain? Raise foundation elevation above high water mark.

❏ Is the floor level? Jack and level on existing foundation.

❏ Are foundation supports in good condition? Repair or replace pads/joists/plywood asnecessary.

❏ Is foundation protected from moisture or wet soils? Raise floor joists at least 8 inchesabove ground—12 inches is even better. Install a capillary break between floor andfoundation.

❏ Is the floor airtight without cracks and holes through the floor? Observe insulationinstallation at perimeter of floor below exterior walls and ensure the cavities are tight andfull to minimize edge air intrusion. Air-seal at all floor penetrations, cracks, and perimeter

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rim joists. Where space does not allow for working from below,airtight insulated skirting may be applied to the exterior of the rimjoist area. Keeping the floor perimeter air tight is the key tocomfortable and efficient floors. Do not interfere with the free flowof air under the house if it is built on permafrost.

❏ Does the floor insulation level meet the BEES R-value for theregion (see Appendix A)? Add fiberglass or cellulose insulationbetween floor joists if space allows. Add rigid insulation to top ofold floor with new plywood above where space does not allowplacing fiberglass or cellulose in joist cavities.

❏ Is the insulation between the floor joists protected from critters?Sheath the bottom of the floor joists with plywood to support andprotect insulation.

Log Wall Assessment

❏ Does air leak in between the sill log and the floor? Caulk and sealthe perimeter sill log to the floor membrane inside the house.

❏ Does the floor protrude beyond the sill logs outside of thebuilding? If so, this shelf area can allow moisture from rain andsnow to enter the structure. Use a wedge of wood cut from 2-by-4or 4x4 to fill this area and caulk the top and bottom to the sill logand floor or use metal flashing to protect the shelf from weather.

❏ Are the logs of sufficient size to provide adequate insulation forthe region? Select a design for increasing wall R-value. Apply wallinsulation and furring to the interior or exterior.

❏ Are joints between the logs tightly sealed and chinked against airleakage? Apply appropriate Weatherall/Perma-Chink typematerial to joints.

❏ Are the logs in good shape around window and door penetrations?Test logs with a probe to determine their condition. Replace ortreat wood at penetrations to prevent further deterioration.

❏ Does air leak around windows and doors? Remove trim andinspect the gap between the rough opening and frame. Removefiberglass chinking and install backer rod and fill cavity withminimally expanding foam if settling is over (older buildings). Airseal the perimeter of windows and doors between the frame andthe rough opening.

❏ Are log wall corner joints tight and sealed against air leakage? Testlog ends with probe and treat to prevent further deterioration. Airseal as necessary with caulks or chinking.

❏ Are the upper gable end wall purlin and ridge penetrations soundand air tight? Use a probe to ensure wood condition is adequate

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for supporting the roof. Apply air sealing measures to penetrationsand purlin and ridge pole ends. Treat logs in these areas as neededto prevent further wood deterioration.

Roof and Ceiling Assessment

❏ Does the roof overhang protect the log walls from rain? Extend theoverhang at eaves to move drip line away from walls and corners.Install gutters and direct runoff away from the foundation area.

❏ Does the top log to ceiling/roof joint show signs of leaking orstaining? Apply air sealing measures to eliminate leakage. Addinsulation as needed to improve thermal properties at thisconnection. Use a probe to ensure wood condition is adequate forsupporting the roof.

❏ Does the roof show signs of water staining or dry rot? Inspect andprobe the wood around chimneys and light (electrical)penetrations. Inspect areas around interior wall connections withceilings. If the house has a cold roof, turn over insulation batts tolocate air leaking from below. These leaks will show as dark anddirty areas in fiberglass batts. Seal air leaks from the attic sideusing acoustical sealant and poly patches. Seal air leaks in hot roofsfrom the interior using appropriate sealants if no major exteriorroof replacement is planned. Treat chimney penetrations withutmost care and concern for fire potential. Replace or reinforce allroof supports that show signs of rot or deterioration. Addinsulation to cold roofs only after all other work has beencompleted. Maintaining an airtight roof and ceiling is critical to thesuccess of any project.

❏ Does the roof exterior show signs of potential leak areas or weatherdamage? Replace or repair shingles and metal as needed to preventwater entry. Replace or repair the flashing around penetrations inroofing. Install eave flashing to “kick” water away from faciaboards.

❏ Does the roof cover all log ends? Cut off all log ends that extendbeyond the drip line of the roof.

❏ Finish interior and exterior of logs as recommended in Chapter 7.

❏ Remember, use all resources available to you to make yourdecisions regarding log retrofits. The AHFC Resource andInformation Center has a library of information available at nocharge (1-800-478-4636). The University of Alaska CooperativeExtension has an energy and building specialist on staff to answeryour questions (474-7201 or 1-800-478-8324). These and otherresources are listed at the end of Appendix D.

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So What Shape isOur House In?

Lower Log Condition

Check all lower logs for dry rot. Thelower logs of buildings in groundcontact will often be rotten beyonduse and must be replaced. This canbe a daunting task that requiresdigging, jacking, and sometimesrebuilding the floor-to-wall connec-tion as the bottom few logs arereplaced.

This may seem difficult, but itcan help extend the life of a poorlyinsulated, energy-wasteful building40 or 50 more years and save energytoo. Where material and fuel trans-portation costs are high, this diffi-cult job will still pay back goodsavings.

Looking for Rot Around

Log Penetrations

Where air leaks occur in buildings,moisture will build up and causerot. Inspect all mechanical andrough opening penetrations beforemaking any decision to retrofit anexisting log house. Use an awl, ice-pick, or a sharp knife point to probethe wood around any opening inthe log walls. Where the wood isrotten the probe will go in easily.Areas of good wood will resist yourefforts.

Usually, the lower openings willcontain rot from outside moisturewhile the upper penetrations willrot from exposure to inside mois-ture. Because windows may letsnow, rain, or ice collect on theexterior sills, be sure to probe theexterior logs in these areas.

A new roof in Arctic Village.

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The lower logs of buildings in ground contact will often be rottenbeyond use and must be replaced.

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If wood around a windowopening is rotten, there are twocommon ways to fix it: Option oneis to make the rough openingbigger if it is possible to cut out therot and make a surface for reinstall-ing the window, and add foaminsulation to fill in the gap.

Option two is to remove andreplace the logs in the area of theopening. This is more expensiveand so takes a longer time to payback.

If two or more windows havesevere rot and logs need to beremoved, go back and look at theproject budget very closely. Thebuilding may not be worth retrofit-ting.

Top Log Condition

The top log (cap log or plate log) isan area where air leaks open upover the years and moisture fromindoors starts wood rot. When thetemperature on the interior surfaceof the log drops, moisture willcollect and possibly freeze on verycold days. This wetting, freezing,and drying cycle promotes rot.

Use the same probing methodto find rot in the logs and framing.You should also check the jointbetween the ceiling and the wall forair tightness and insulation.

This cabin was almost destroyed by rot.

The cabin was saved by cutting out all four log corners andinstalling large vertical log corner posts. A good solution to useas much of the old building as possible. Note the trimmed rooflogs and shorter porch.

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One way to fix the top wall logto ceiling joint is by sprayingseveral inches of a two-part ure-thane foam into the wedge formedby the wall and ceiling (see illustra-tion, page 81). Then add a vaporbarrier (usually polyethylenesealed with an acoustical sealant),and finally cover it with a nice trimboard.

Let’s Start at the BottomIf you have enough room, a popu-lar way to add insulation to thefloor is to cover the existing floorwith rigid foam, and cover thiswith plywood.

In many projects we have usedtwo-inch extruded foam (usuallyblue, pink, or green) for the insula-tion overlay. This rigid insulation

has a high compressive strengththat makes it suitable for suchinstallations. The covering plywoodmay be 3/4" tongue and groove. Usea structural adhesive and apply it toall plywood edges, including thetongue and groove, to construct anairtight floor membrane. Seal thejoint between the perimeter ply-wood and the log wall with adurable polyurethane caulk. Dry-wall-type 3 1/2-inch screws are usedto fasten the plywood through thefoam, resulting in an additionalR-10 insulation, an airtight floor,and a new durable surface for thefinished flooring.

The negative associated withthis approach is that rigid foaminsulation is a higher cost perR-value insulation than “soft”insulations (fiberglass) and the

This floor is accessible and has floor joists that are deep enough for the minimumamount of insulation (see Chapter 3).

no insulationat rim joist

air gap aboveinsulation

rotten or collapsedframing, causing floorto sag

critters have easy access todamage insulation

Some Problems to Look For

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new flashing

new rigid foamaround theoutside of thefoundation

new two-partfoam sprayedon the rim joist

new fiberglassinsulationinstalled tightlyup against thefloor, with no airpockets new sheathing to keep

out animals

bottom logsealed againstair leaks withcaulk

A large part of the decision to fix the old floor and reinsulate or build up the floor from the inside of thehouse depends on whether you can even get under the house. It is usually more labor to go under thehouse and fix the old insulation, but the materials can be cheaper.

Observations from Arctic VillageSometimes, people cut logs in the spring and summer and then build with themin the fall. The logs may be only partially peeled or not peeled at all in somecases. When they build a house with logs like this, large cracks will develop inthe logs after one year. First as the house is heated through the winter , thecracks will appear on the inside, and then the following summer as the sunheats the exterior, the cracks will appear on the outside. Eventually cold air willbe able to travel completely through the cracks into the house, making thestrucure very leaky .

Another problem that results is that the cracks and unpeeled areas willcatch rain and snow, which will eventually rot the logs. This will speed up theprocess of failure of the bottom logs that are providing the foundation, whichin turn will help to destroy the rest of the building. Homes that are built in thismanner are falling apart much faster than they should.

(comments from local resident, collected by Mimi Burbage)

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tongue and grooveplywood caulked atall joints.

rigid foam insulation fittedtightly between new 2-bylumber cut to make a levelfloor

gaps in a severely warped floorfilled with soft insulation

plywood sealedto bottom log

In spite of the insulation cost, it is less labor to install the insulation above the floor than work-ing below the floor, framing additional cavities and making other labor-intensive modifications.

rigid foaminsulation

Seal the jointbetween theperimeterplywood andthe log andbetween sheetsof plywood.

glue designed foruse with foam

Don't line up plywoodjoints with foam joints.

Here is an example of adding rigid foam to the top of the floor without any additional framing.Be sure to stagger the joints of the foam so they don’t line up with the joints in the plywood.

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A three-sided log wall retrofitted with astand-off wall, a good continuousvapor retarder, insulation, and siding.You can also use a 2-by-4 wall with6 inches of insulation packed to fill inbetween uneven logs.

added floor thickness of 2 3/4 inchesmakes adjustments to doorwaysnecessary. However, in spite of theinsulation cost, it is less labor toinstall the insulation above thefloor than working below the floor,framing additional cavities andmaking other labor-intensivemodifications.

Exterior Wall RetrofitThe most energy-efficient way toretrofit a log home is to attach aninsulated curtain wall on the

outside of the logs. This leaves themassive logs on the inside of thethermal envelope and provides veryeffective thermal storage. Once thelogs are heated to room tempera-ture, it may take days without heatfor the logs inside the thermalenvelope to cool off, even in anAlaskan winter.

An exterior retrofit of a loghouse typically involves chainsawing off the log extensions at allcorners of the building. Do notcompromise the structural integrity

6-mil polyvapor barrier

insulation

siding

add a Tyvek or other brandair/weather barrier betweenthe insulation and the siding

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of the house by cutting off toomuch. The objective should be toremove any corner log ends thatstick out beyond the curtain wall tobe attached. Remove any otherprojections that would interferewith wrapping the exterior of thelog walls with a continuous 6-milpoly vapor retarder. Pay particularattention to sealing the vaporretarder at the top and bottom andat all window, door, and utilitypenetrations.

Since log walls are irregular, itwill be necessary to fit each stand-

off stud with a system of blockingand plywood gussets attached tothe logs on two-foot centers. Firstestablish the corner stand-off studsplumb and at a distance from thelog wall to accommodate the de-sired thickness of insulation. Use astring line pulled tight between thecorner studs to establish the align-ment of all the rest of the studs.Sometimes the roof rafters cansupport a hanging curtain wall. Ifthe house has not completely settled(8 to 10 years in a dry climate), thenbe aware that the roof is still on its

vapor retarder

insulation

Tyvek or otherbrand house wrap

siding

two optionsfor stand-off wallattachment

slot toallow forsettling

cover bottom tokeep critters out

Exterior Wall Retrofit

6-milpolyvaporbarrier

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way down and attach the studs andthe bottom plate in a manner thatwill allow for settlement.

It may be a good idea to wrapthe insulated stand-off walls with aweather retarder house wrap suchas Tyvek or Barricade before install-ing horizontal beveled or rough-cutspruce siding. The bottom of thewall should be covered with flash-ing, plywood, or dimensionedlumber to keep little creatures out.

Interior Wall RetrofitAs stated in the introduction, aninterior retrofit of a log home turnsthe logs into very heavy and expen-sive siding, with all the thermalmass on the outside of the thermalenvelope. Nevertheless, it is verycommon to fur in, run electricalwiring, and insulate and vaporbarrier walls constructed of small-diameter logs. This does indeedimprove the thermal performanceof the wall, not only by increasingthe R-value but also by reducingthe air leakage.

The interior retrofit also reducesspace and can make a small cabininto a really small cabin.

A simple way to add R-value tothe inside without a lot of fasteningproblems is to use 2-by-4 studs andplates on the inside of the exteriorwalls. These should be installedtight to the logs and plumbed.Some shimming or shaving may benecessary to achieve a fairlystraight wall, but this will dependon the quality of the original con-struction.

After the wall is fastened inplace, use 6-inch fiberglass insula-

Sheetrockvaporretarder

Caulk vapor retarderto subflooring

caulk vapor retarderto subflooring

vaporretarder

slots

washer

Attaching an interior wall to a three-sided log exterior wall with a 2-by-6

Interior retrofit on a log wall

attach to log wall withslots to allow settling

6-inchfiberglassinsulation

2-by-4 stud

2-by-6 stud

airtight e

lectrical

penetratio

ns

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tion and pack it into the stud cavi-ties so that it fills the cracks be-tween the logs and provides a goodfriction fit. Even though the insula-tion is compressed in some areas, itwill still provide good insulatingqualities since it will fill the voidsadequately.

Install airtight electrical andmechanical outlets before installingthe air-vapor barrier.

Roof RetrofitIf the finished ceiling is still in goodshape but the roof is under-insu-lated or needs a vapor retarder, youmay consider cutting off the eaveswith a chain saw at the outside ofthe logs and running the newexterior wall vapor barrier of6-mil poly up the wall and over theold roof and down the other wall.The gable-end wall vapor retardershould be caulked at the jointbetween the log and the ceiling aswell as where the log meets thefloor at the bottom of the wall. Lapover and seal the vapor retarder tothe other sheets of poly at the fourcorners.

Place this exterior 6-mil polyeth-ylene wrap on the warm side of thethermal envelope. Whether in thewall or roof system, at least twothirds of the R-value must be on thecold side of the vapor retarder tokeep the humidity in the air warmenough so it doesn’t condense intoliquid water inside the wall or roof.Build up a new roof on top of theold, taking care to protect the vaporretarder during construction.

Remove the old roof down tothe ceiling boards. If the ceilingis still in good shape it can beused again without removing.This allows the building to beoccupied while the roof is beingreplaced.

Saw off the remainingoverhanging ceilingboards.

Wrap the house with acontinuous vapor retarder(6-mil poly or better). Careand craftsmanship arestressed at this point to geta good sealing ballooneffect to keep in warm air.

Add an exterior wall with avapor retarder and insula-tion. Observe the 1/3–2/3 rule(see opposite page).

vaporretarder

oldinsulation

new vaporretarder

air space

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Hot Roof Retrofit If you put a new air barrier ontop of the existing roof, and moreinsulation and roofing above it,then the building science one-thirds/two-thirds rule must berigidly adhered to. This rule helpsyou locate the air/vapor retarder ininstances where the barrier mightbe placed between two insulationlayers. If there is an air gap over theold insulation, pack the area abovethe outside walls to maintain acontinuous blanket of insulation onall six sides of the house: four walls,floor, and roof.

Hot roofs are typical in log build-ings with traditional purlin andridge pole exposed ceilings. Herethe insulation is installed betweenthe roof rafters. By definition, thehot roof does not provide ventila-tion. It usually has no access forinstalling additional insulation.Ventilated hot roofs are beingconstructed on newer log build-ings, however, this is a recentdevelopment and it is rare to findsuch designs in older log cabinsand houses.

You must first determine whichsurface to add the insulation to,inside or outside. If the roof con-sists of leaky shingles and rottenplywood, the obvious area tomodify would be the outside. Stripoff the shingles, install a vaporretarder, put insulation on theoutside of the vapor retarder, andreinstall roofing.

The inside is a better approachbecause it is easier to get an airtightinstallation. Framing additionalceiling surface supports and insu-lating between the top log andpurlin and between the purlin andridge pole have proven successful,although this covers most of the logceiling and may not appeal to someowners.

It is most important to locatethe surface that will serve as the airbarrier or vapor retarder if you putmore insulation on the outside of ahot roof. If it will be the interiorsurface, great care must be taken tomake it truly airtight, because if airleaks into the roof, the moisturecarried in the air will damage theroof.

At least twothirds or more ofthe R-value mustbe on the coldside of the vaporretarder. In thefar north, at leastthree quartersshould be on thecold side.

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An interior retrofit of a ceiling in progress; note new electricalwires being installed.

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vapor retarder stopsmoisture-laden air fromentering wall space

dew point temperature

vapor retarder

dew point temperature

moisture-laden aircondenses inside wall,causing damage

Cold Roof RetrofitWe typically call a truss roof a coldroof because the space above theinsulation is ventilated to theoutside. While not always venti-lated, this attic space is designed tobe significantly colder than a hotroof, where ventilation space isminimal or nonexistent. The coldroof can receive more insulationsince space is usually available.

Before putting more insulationin the attic, seal all ceiling and atticpenetrations to prevent any airleakage from carrying moisture intothe attic space. This is usually donefrom the attic (top) side by findingeach leak and applying a heavybead of acoustical sealant aroundthe penetration and embedding apatch of polyethylene into thesealant. Tape this patch in place so itwon’t move around. Do this to allpenetrations and breaks in the air/vapor barrier, including partitionwalls. This is not the place to skimpor save on acoustical sealant.

After all air sealing has beendone, you should measure thedistance between the outside edgeof the wall and the underside of theroof plywood or metal. If roomexists for meeting the minimumrecommended BEES insulation,then proceed with putting newinsulation in place. However, mostolder roofs don’t have enough spaceto allow for high levels of insulationover the wall. Use a rigid insulationthat has a high R-value per inchsuch as foamboard where space istight. Cutting the rigid material to

What’s a Dewpoint ?The dewpoint is the temperature atwhich moisture condenses from vaporinto water. Water vapor in the air inthe house gets cooler as it moves outthrough the wall and roof, and atsome point it condenses. If this temp-erature is inside the wall of the house,it will cause rot. This is why at leasttwo-thirds of the R-value of yourinsulation must be outside of thevapor retarder. In the far north atleast three quarters should be on thecold side.

Water vapor inthe air getscooler as itmoves outthrough the walland roof. If itcondenses insidethe wall of thehouse, it willcause rot.

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vaporretarder

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One way to fix the joint between thetop wall log and the ceiling is byspraying several inches of a two-parturethane foam into the wedge formedby the wall and ceiling. Then add avapor barrier (usually polyethylenesealed with an acoustical sealant), andfinally cover it with a nice trim board.

ceiling boards

trim board

fiberglass

rigid foam2x4 nailer

two-part foam plate log

vapor retarder

vapor retarder

air space above insulation

fit tightly into the cavity is impor-tant! By placing three layers of two-inch polyisocyanurate rigid foaminsulation (R-48), you can comecloser to meeting the minimumrecommended BEES standards thanwould be possible using soft insula-tions (fiberglass) in this tight spaceover the wall.

Chimney and FluePenetrationsThis is an area of frequent failure inall types of roofing. There are twopotential problems: chimneyslocated too close to wood are a firehazard, and leaks can develop inthe roof around chimney penetra-tions, leading to rot.

Research has shown that whereheating appliances are near wood, asignificant drop in the wood igni-

tion temperature occurs. It willignite and burn easily at muchlower temperatures.

Maintaining a good air gaparound the insulated pipe above theceiling is also necessary, and more isbetter here. If the attic contains lotsof insulation, you should extend theinsulation dam (a sheet-metalcylinder around the chimney) toprevent insulation from getting intothe air gap surrounding the chim-ney. The dam should always be leftopen at the top to allow air currentsto cool the space between the damand chimney. Always follow themanufacturer’s instructions. Justfollowing codes and regulationsmay not be enough to prevent thewood framing from turning intofuel.

Chimneys typically found inolder buildings must be improved

rigid foam in truss-style roof with attic

sub-standard truss

batt orblown-ininsulation

stack rigid insulation

vaporretarder

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Sheetrock

sheet metalflashing

trim collar

single-wall pipe toheater (typical)

vaporretarder

18"

attic

high-temperature RTV silicone

metalinsulatedchimney

extension to metal insulation dam

metal insulatedchimney

at least2" air space

Sheetrockacoustic sealanttrim collar

single-wall pipe toheater (typical)

attic

high-temperature RTV silicone

18"

metal insulatedchimney

metal insulatedchimney

extension to metal insulation dam

at least2" air space

This stove pipe and chimney areoverdue for a good safety upgradeand retrofit.

Attic side air seal (typical on new construction) Interior side air seal (typical on retrofit)

This is an example of a proper installa-tion of a chimney and stove pipe.

acoustic sealant

to prevent moisture from enteringframing members in the roof andceiling. Therefore, care must betaken to eliminate all air leakagearound chimneys. See the illustra-tions for examples of how to do thissafely.

Note that different caulks andsealants are used to provide for acomplete and airtight seal aroundthe chimney and to the surroundingdrywall. Use a high-temperatureheat rated RTV silicone caulk forair-sealing the trim ring to theinsulated chimney.

slip joint permanufacturer’srecommendation