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Backfillingan essential step in basement con-s t ructionis all too often the beginning ofbasement destruction. Done impro p e r l y,backfilling causes problems that may start be-

f o re the b uilder leaves the site and may remain longafter hes gone. But the problems can be avoided by tak-ing a few simple precautions.

T h e re are four key elements to proper backfilling: Protecting the foundation wall from damage duri n g

b a c k f i l l i n g Using the right backfill materi a l s Compacting the backfill Final finishing the subgrade to ensure that water

d rains away from the foundationDone corre c t l y, these four steps help to ensure that a

well-built basement functions the way its supposed to,p roviding the homeowner with dry, usable living space.

Protecting the wall during backfilling

The surest way to protect walls from damage duri n gbackfilling is to backfill only after the basement floorslab and the first-floor deck are in place. For the deck,sill plates should be bolted down and joists nailed to thesill plate. This provides the re s t raint needed to make the

wall strong enough to resist earth pre s s u res caused byb a c k f i l l i n g .

Home builders seldom want to wait until the deck isin place, howe ve r. Early backfilling speeds the fra m i n gp rocess by making the foundation more accessible forcarpenters so they dont have to ramp in.

An altern a t i ve is bracing the walls before the deck isbuilt. We do this for all straight walls longer than 24 feet

that dont have offsets or pilasters. Co rn e r s, offsets, andpilasters add stru c t u ral stiffness to the foundation wall.But we figure as a rule of thumb that the stiffening effectis negligible more than 12 feet away from the corn e r.Hence straight spans longer than 24 feet need bra c i n g .

We use ve rti cal bracingsteel braces fab ri c a t e df rom 3-inch-diameter schedule 40 pipewhich wequick-bolt to the wall and slab or pier pad as shown inFi g u re 1a. We also modify some shoring jacks from af o rm manufacturer to do the same thing. Another op-

BackfillingbasicsBackfilling the wrong way often costsmore than doing it right

BY R. T. BUCK BARTLEY

Figure 1. Vert ical or horizontal bracing can be used t oprotect walls from damage during backfilling. Verticalbraces can be made from steel pipe (drawing a) or lumber(drawing b). Horizontal bracing (drawing c ) works well forstraight walls up to 48 feet long.

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tion is bracing with lumber usingscaffold boards or 3x12s as show nin Fi g u re 1b.

If the slab and pier pads cant beused for bracing, hori zontal bra c i n gas shown in Fi g u re 1c is usually ad-e q u a t e. Attac h 3x 12s to all fourw a l l s, parallel to and about 4 feet

a b ove the footing. Then toenail3x12s diagonally across the corn e r sas shown. Add 2x4 cleats and kickersto pre vent slippage and flex. Thissystem works well for walls up to 48feet long. Be yond that length addi-tional intermediate ve rtical bra c i n gis needed, attached to pier pads,

f o o t i n g s, or wood

stakes firmly dri-ven into theg ro u n d .

Although mostbuilding codesre q u i re thatfoundation wallsbe adequatelyb raced beforebackfilling, mosthome buildersd o nt use bra c e sfor poured con-

c rete walls. Theyb e l i e ve that thec o n c rete is stro n genough to re s i s tp re s s u re causedby backfilling.And they may getby without dam-aging the wall.But too often awall gets pushedin (Fi g u re 2).Sometimes this

happens duri n gthe winter whenc o n c rete doesntgain stre n g t hquickly becauseof low tempera-t u re s. So m e t i m e si ts because the ex-c a vating contra c-t o rs equipmentgets too close tothe wall. Andsometimes ra i ns a t u rates the are aa round the foun-dation soon afteri ts backfilled, in-c reasing soil pre s-s u res enough tocause a wall failure.

W h a t e ver thec a u s e, the homebuilder is left with

a costly problem. Fixing it will re-q u i re pushing out the bow in thewall and re p a i ring the crack withe p oxy injection. As insura n c eagainst a wall failure, having twocarpenters work a couple of hoursb racing the wall is a good inve s t-m e n t .

Choosing the right backfill ma-

terial

Some people recommend back-filling with a fre e - d raining gra n u l a rm a t e ria l. Im not so sure thats al-ways a good idea. When you dig ahole in the ground for a foundation,water moves tow a rd the hole just asit does in a well. A granular fillmakes it easier for water to move to-

w a rd the foundation wall. And if thed rain tile system gets plugged, thatcould cause pro b l e m s.

I think the object should be to re-s t o re equilibrium, as nearly as pos-s i b l e, to the soil moisture system.That usually means putting back inthe same soil that came out. But notif its a poor soil. If heavy, moisture -laden, or expansive clays are re-m oved during exc a vation, gra n u l a rbackfill with an exterior dra i n a g esystem would be the best choice.

Also avoid backfilling with larg eclumps of clay or with soil full ofro o t s, tree bra n c h e s, or other org a n-

ic materials (Fi g u re 3). These mate-rials wont compact well and willhold a lot of water even if theg round slope is steep enough to car-ry surface water away from theh o u s e.

The amount of ove rdig for a foun-dation is about 3 feet. Splash blocksfor downspouts dont usually carrywater more than a foot or two awayf rom the foundation (Fi g u re 4). Somost of the water that comes off theroof may still end up next to thefoundation if the backfill is poro u s.

Compacting t he backfi l l

As backfill soil settles, dra i n a g ep a t t e rns change and water may flowt ow a rd the house or pond next tothe foundation. Compaction isneeded to reduce the amount of soilsettlement that occurs with time.

Fa i l u re to compact the soil can

Figure 2. Bac kfilling pushed in t his unbraced wall andcracked it . The diagonal crack w as repaired by the homebuilder but t he wall stil l leaked when the owner moved in.Fixing the problem required excavation, pushing out thewall, and installing new waterproofing at a cost muchgreater than doing the job right the first time.

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cause basement leakage even be-f o re the ho use is compl eted. Fi g-u re 5 shows the results o f poorg rading and no backfill com-paction. In this case, during ra i n ywe a t h e r, wat er col lected in the

t rough caused bysettlement ands t a rted lea kingt h rough shr i n k-age cracks in thefoundation wall.Co r rect ing thefaulty dra i n a g estopped the

leaking .Be careful whencompacting back-fill. Some com-pactors are powe r-ful enough todamage the wall.One way to avo i dthis problem is toplace the backfillin 6-inch-thicklifts and have thel a b o rers tamp it

with foot pre s s u reor hand ra m m e r s.Vi b rating platecompactors alsocan be used forg ranular backfillwithout damagingthe wall. It takesm o re time to com-pact thin laye r s,but the methodp rovides insur-ance against wall

damage andagainst call-backsrelated to dra i n a g ep ro b l e m s.

Final finishingto t he correctgrade

Di ve rting sur-face water awayf rom the founda-tion is one of themost effective

ways to pre ve n tbasement leak-a g e. The mini-mum slope for

finished grade should be 1/2 inchper foot for at least 10 feet awayf rom the foundation. This is espe-cially important if there are land-scaping beds near the house. Wa t e r-ing plants in low-lying areas close to

the foundation saturates the soiland makes basement leakage morel i k e l y.

If the house is set high enough onthe lot, getting the correct grade ford rainage isnt difficult. Too often,h owe ve r, houses are built too low.Then instead of the code-re q u i re d8-inch minimum between the sill

plate and exterior grade level, thehouse might be built with the fin-ished grade only 4 to 6 inches belowthe plate. To ave rt this pro b l e m ,a void making the exc a vation toodeep and set footing elevations highe n o u g h .

Avoiding basement leakage is alot like pre venting a roof from leak-ing. You need to keep the waterm oving and pre vent it from collect-ing in one spot. Co r rect backfillingmethods help to accomplish this

goal.

Buck Bartley is a general contractorin Silver Spring, MD. Hes a forme rp resident of the Poured Concre t eWall Contractors Association, nowcalled the Concrete Foundation As-sociation.

Figure 3. Back filling wit h soil full of tree roots leaves aporous fill that can cause basement leakage. The fill cantbe properly compacted and will settle with time.

Figure 4. Splash blocks oft en dont carry wat er fromdownspouts beyond t he backfilled area. Then water fromthe roof saturates the backfill.

Figure 5. Sett lement c an occur rapidly in poorly compactedbackfills. Water collecting in the low spots may causebasement leakage even before the house is complet ed.

Publication # C910315Co py right 1991, The Ab e rd e e n

Gro u p. All rights re s e rve d