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If you do the layout

carefully and precut

all the joists, the floor

will go together

quickly like a giant

jigsaw puzzle

by Rick Arnold and Mike Guertin

W e've finished backfilling the foundation, andthe mudsills are level and square. Now the realfun begins: saws screaming, hammers humming,sawdust flying. But as anxious as we are to shiftinto high-gear production mode, we always ap-proach the task of floor framing methodically andthoughtfully. With this strategy, everything goes to-gether right the first time, and the reciprocatingsaw and the cat's paw stay in the toolbox wherethey belong.

A good framing plan streamlines layout andinstallation Beforewe even think about gettingour tools out, and usually before breaking ground,we start our floor on paper with a framing plan(drawing p. 54). Most of the house plans we workfrom do not include a framing layout, so usuallywe create our own.

First, we choose the best starting point for thejoist layout to minimize the number of joists andthe subfloor waste. After looking at how the houseis laid out (where the jogs are; how the roof trusseswill be laid out; where bearing walls are; wheretoilets, tubs and showers fall), we decide where tobegin the layout. With the house featured in this

article, the natural starting point was the front leftcorner because of the two adjoining sectionswhere the joists changed direction. When indoubt, we usually pick the 90 corner that has thelongest uninterrupted legs. All smaller sectionsare then blended into the larger layout.

On our plans we draw lines for each joist, head-er, in-floor beam and any special framing detailsfor the house. By using a different colored pencilfor each joist length, we can use the plan for ac-curate material ordering later. When materials aredelivered, the joist plan also enables us to directthe different-length 2xs to the appropriate areasof the floor with just a glance.

We try to have a preliminary meeting (or at leasta couple of quick faxes) with the plumber andheating contractor to identify any joists that mightpose a problem with their systems. We can alsoalert each contractor if we see that both of themexpect to fill the same joist bay. By moving a joist acouple of inches to one side or to the other, wesometimes can resolve competition for space. Wegenerally try to avoid having a joist positioned di-rectly below a wall above, and knowing which in-terior walls will contain vents, drains or ductwork

keeps us from placing a joist where it mighto becut.

The big exception to that rule is where the has bearing walls running parallel to the joists. In those cases we usually double orjoists under the bearing wall to carry the wHowever, if a plumber or HVAC sub plans tobearing wall for drains or ducts, we identiexact location of the wall on our plan and the joists under the outside the edges of theSolid blocking is then installed between theevery 2 ft. or so, leaving space for the systcome through. We also double the joists belarge tubs or whirlpools if the fixture is to simiddle of the joist span.

Floor details are spelled out in the layoutOnce the foundation is poured and backfilletake great care installing and adjusting mu(FHB#97, pp. 46-51), carrying beams and ment bearing walls. As we prepare for the everything is kept level and square, and tmensions on the plans are matched exactly.closer that we keep the tolerances at the deck stage, the quicker and easier the rest o

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Assembling the floor frameThe best floor layout begins on paper. B e fo re any lumber is ordered, a detailed fram ing plan should be drawn. The fram ing plan exposes potential proble m areas such as b earing w alls, plum bing or floor openings that might require special attention, and the color code (inset) indicates joist lengths for ordering and then precutting lum ber when it arrives.

String keeps the layout uniform. The bluestring in the foreground was stretched between thelayout marks on the sills. Measurements on the car- rying beams are then taken from that line.

house framing will proceed. Before beginningour layout, we string the carrying beams andbearing walls and brace them to keep themstraight. These strings are left in place so that wecan double-check the walls again after the joistsare installed.

To ensure consistency, one crew member does all the joist layout. We begin our layout bymarking any special features of the floor deckthat interrupt common joist layout. In additionto the chimney and stair openings, the projectfeatured in this article had a cantilevered sec-tion, in-floor beams and two areas where thejoists change direction.

These special details and measurements aremarked with a lumber crayon on the sill platesto alert the crew that the standard layout haschanged. Someone following the layout personcan then precut the odd pieces, and the instal-lation is easy and obvious. By the way, if anopening in the floor happens to cross a carry-ing beam, we snap lines across the beam fromthe marks on the opposite sill plates to keep our

measurements consistent.

Make sure the "X" is on the right side of line With all the special features of the decklaid out, the next step is laying out the commonjoists on the sill plates that run perpendicular tothe joists. This floor called for 2x10 floor joistslaid out on 16-in. centers.

Starting from the end we determined on our plan, we make marks in. shy of each 16-in.symbol on the measuring tape. When the entiresill plate or beam is marked off, we go back andmake a square line at each mark and draw an X forward of each line. The same procedure is re-peated on the opposite side of the house startingat the same end.

Next, we run a line between our starting markson the sill plates across any intermediate bear-ing walls or beams. This line gives us a referencepoint from which to lay out the tops of the bear-ing walls or the carrying beams (photo above).The uniform starting point helps to keep thejoists in a straight line and makes it easy to laydown the subflooring later. Walls and beams arethen measured and marked at 16-in. intervals

from that point.

The main body of the floor featured in thisticle is 44 ft. deep. The span is broken into t14-ft. sections and one 16-ft. section. The joisthe front section will be set ahead of our maas indicated by the Xs. The middle section wbe set behind the mark, and the rear sectibe set ahead of the mark like the front. The toutside sill plates get only one line to indicthe location for each joist. Bu t on the two innal beams where joists from adjoining sectiowill overlap, we add additional lines indicatithe outside edges of the joists. (Because we tnail the overlapping joists to the beam after bojoists are in place, a single layout line wouldhidden beneath the joists.)

Careful attention is paid to crowns Whileone crew member works on the layout, anothsorts and crowns the joist stock (photo bleft, p. 52). We use only kiln-dried lumber floor joists. Kiln-dried lumber is less likely tgreen lumber to shrink or to change shape ovtime. And because kiln-dried lumber

preshrunk, we don't get problems usually ass

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Rim joistgoes on first.Before anycommon joistsare installed, arim joist or band joist isnailed to theouter edge ofthe mudsills.While onecrew member assembles therim, another transfers thelayout up fromthe sills to theinside face ofthe rim joist.

Taking the crown out of a rim joist. If arim joist has a severe crown, a relief cut ismade that allows the joist to be drawn all theway down to the sill or plate.

Rolling the joists into place. After the joists are laid in flat, a crew member rolls them onto their layout marks and nails them to the rim.

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Floor frame (continued)

Squash blocks carry loads fromabove. Two-by blocks called squash blockscut slightly longer than the height of thejoist help to transfer loads directly to thesill plate or carrying beam. Here, thesquash blocks are installed under header- bearing jacks for a sliding door above.

Tweaking the rim joist. Before the sheathing goes on, a string is run along the top edge ofall the rims that run perpendicular to the joists. The rim is tapped in or out and checked witha square until it is perfectly straight.

dated with green stock, such as drywall cracks,cracked tile, and doors and windows that bind.

Every piece of sawn dimensional lumber has acrown, or a natural curve it takes on after it is cutfrom a log. We look at each floor joist and markthe direction of its crown with an arrow (photobottom center, p. 52). Those with excessivecrowns (more than in. in 8 ft.) are set asideto be cut into window or door headers later.

When we get a unit of joist stock that has manyboards with crowns of more than in., we gradeeach joist with an A, B or C designation. Withoutthis extra effort, we could end up with large dif-ferences between adjacent joists, creating awashboard effect in the floor and making it dif-ficult to install the tongue-and-groove sheathing.In those cases, the straightest A-joists are used asrim joists and beneath tiled areas such askitchens and baths. Floor sections that will becovered with hardwood receive B-joists, and C-joists with the b iggest crowns a re saved for floor

areas under carpet or to be cut into headers.

The rim is installed first The rim joist or band joist is toenailed to the outer perimeter ofthe floor on top of the sill plates or to the topplates of exterior walls (top photo, p. 55). Weuse 16d nails every 12 in. The rim joists that runperpendicular to the layout prevent the floor joists from rotating. Rim joists that run parallel tothe layout close off the floor area along its out-side edge. We also install band joists at the inte-rior transition points where joists change direc-tion. Here, they serve as a break point for theedges of the sheathing as well.

We select straight stock for the rim joists so thatthe crowns don't leave a space between the rimand the plate. If such a space is left, the rim willeventually settle under the weight of the houseand cause problems later. When straight stock isscarce, we make a sawcut near the middle ofthe rim joist about two-thirds of the way acrossthe board (photo bottom left, p. 55). The cut ismade in the direction of the crown and lets usfasten the joist down all the way to the plate.

We use the rim joists as in-floor headers ovwindow and door openings in framed wallwherever possible. In-floor headers let us skthe traditional headers and jack studs for opeings in exterior walls that run parallel to the jodirection. As long as the rim doesn't break ovthe opening, a single rim joist can carry the wweight above short openings. For wider such as over a sliding door, we double up thrim over the opening.

This method uses a little less lumber framinand more important, it increases the thermal eficiency of the wall. On this house we eliminat24 jack studs (or 3 ft. of solid wood in the waand 36 ft. of header stock. All this space cnow be insulated.

Common joists are rolled into place Weused to take care to cut the rim-joist stock break exactly on the center of a floor joist. Bbecause the structural wall sheathing exdown to cover and secure the joint, there isn

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Laying down the sheathing

any real benefit in doing so. We do check theend of every rim joist to make sure that it'ssquare and trim it if it's not. Square ends are es-pecially critical at the corners to maintain theexact dimensions of the floor deck. Once all therim joists are in place, we use a framing squareor a triangular rafter square to square up all thelayout lines from the sills or basement wall

plates onto the inside of the rims.The crew member who crowns the floor joistsalso checks the end that will butt against the rimjoist for square. At the same time, framing mem-bers for floor openings are cut from the mea-surements written on the sill plates and thengrouped into kits (photo bottom right, p. 52).For example, the kit for this house's chimneyconsisted of short rim-joist pieces, headers andcripple joists. When the kit is finished and eachpiece is clearly marked, it is neatly stacked out-side the foundation close to where it will be in-stalled. In areas where joists change direction,

the joists have to be cut to length to fit between

two rim joists. After being cut, these joists are al-so stacked near where they will be installed.

We usually assign one crew member to as-semble and install the kits for rough floor open-ings, and the rest of the crew installs the com-mon joists. We first lay all the joists flat on the sillplates and across the carrying beams with allthe crowns facing in the same direction (top

photo, p. 52). Now we can walk along the out-side of the foundation or on top of the platerolling the joists into place and nailing them tothe rim (photo bottom right, p. 55).

If a joist is shorter in height than the rim, we liftand nail it flush with the top of the rim. We goback later and shim under all the short joists.After a joist is nailed through the rim with four or five 16d nails, we drive three toenails throughthe joist and into the mudsill or top plate. At thispoint, however, we don't nail the joists at thebeams or bearing walls.

After all the joists are nailed in place, we

recheck the strings that we set up earlier to

straighten all the interior carrying beams awalls as well as any exterior framed walls. Wwe're satisfied that everything is straight, walk the beams and nail the overlapping joito each other again, flushing the tops and shming under short joists. The overlapping joare fastened to each other with four or five ndriven at an angle so that the nail points do

stick out the other side. The joists are nothe outside lines we drew earlier and toenailto the b eams or wall plates with four na

According to code (CABO 502.4.1,1995), ejoist must bear a minimum of in. wheon a carrying beam, and there must be a potive connection at the joist laps. There are thbasic ways to make an approved connectiobetween joists that overlap. The most commway to connect opposing joists is by overlping them a minimum of 3 in. Another methis using either a wooden block or steel ctor plate as a splice across the joist joint. T

third method is letting the subfloor sheathi

A single nail keeps the joist on the layout. After the sheethas been tackedat thecorners, a tape is hooked on the joist tacked to the she athing, and the other joists are moveduntil they fall into position. A single nail is then driven to hold the joist on the layout.

A sledgehammer snugs the sheathinginto place. A 2x block protects the grooves

in the edges of the Sheathing as it is tappedinto place with a sledgehammer.

Start spreading the .glues. A generousbead of construction adhesive is spread oneach joist and on the plywood edge.

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Sheathing (continued)

span across the intersection of the joists by aminimum of 3 in.

We never use solid blocking between joistsover the beams or bearing walls to transfer loads. Instead, we frame all our walls so that thestuds line up directly over the joists. Wherever we have concentrated loads falling on a joistfrom a wall above, such as jacks carrying a load-bearing header, we install squash blocks, a tech-nique we borrowed from our engineered-I-joistexperience(FHB#108, p. 53). Squash blocksare 2x blocks cu t slightly longer than the heightof the joist. They are installed on end beside thejoist to help transfer loads to the sill plate or car-rying beam (photo left, p. 56). Usually, we in-stall squash blocks after the floor is sheathed,unless we can pinpoint bearing points before.Since we began using squash blocks in conven-tional floor decks, we've virtually eliminated dry-wall cracks around door and window openings.

Don't skimp on the glue for the sheath-ing When all the joists are fastened in place,

we double-check all the floor-deck dimensions

and take diagonal measurements to make surethe deck is square before we start installing thesubfloorsheathing. If the rim joists were installedwith square ends at the corners, our measure-ments are usually close. If the diagonal mea-surement is off more than in., we tweak therim in or out to make the adjustment.

Next, we run strings along all the rim joists run-ning perpendicular to joist runs. We tap the topof the rim in or out as needed and shim if nec-essary to get the rim joist perfectly straight (pho-to right, p. 56). Squaring the joist ends helps tokeep these adjustments to a minimum. Rimsrunning parallel to the joists will be straightenedlater after the sheathing is installed.

To begin sheathing the deck, we measure 4 ft.in at both ends from our starting edge, usuallythe front of the house. We snap a line and startpumping adhesive onto the joists. From therewe snap lines every in. for a glue guide for each row of sheathing. (We use a -in. mea-surement because the tongue and the groovecost us in. for each row of sheathing.) The

snapped line tells us where to stop the glue for

each row to keep glue off our tapes and to kethe joists beyond the sheathing safe to st

The first set of sheets is set with the tongon the rim joist so that we don't ruin them whwe bang the sheets into place on successivrows. The first course of sheathing is nacompletely with 8d ring-shank nails so thadoesn't drift when we drive the next set of shein place. We don't glue or nail the edges of tsheets along the rim joist running parallel to tjoist direction so that it can be straightene

Spreading glue on the joists is an ofteoverlooked operation. However, we take ougluing seriously. We probably go through mamore tubes than most crews, but we belieworth the extra labor and material.

Each joist gets a generous bead of glue, anthe section of joist where two panels meet getbead along both edges of the joist (photleft, p. 57). We also run a bead of glue down tgroove before installing the next row of sheeThe glued tongue-and-groove seams are mustiffer and squeak-free than those left dr

when glued properly, the sheathing function

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as a vapor barrier, provided that all utility pene-trations are carefully sealed.

Framing crews usually just flop the sheets ofsheathing down haphazardly onto the joists andslide them over into position. In the process, theglue is smeared and rendered useless, and thejoists become a sticky, slippery mess. Instead,we try to lay each sheet down as close to whereit is supposed to go and as carefully and gentlyas possible, which keeps the glue bead where itbelongs and keeps the work area neat and safe.

As each sheet is laid down, it is tapped againstthe adjacent sheets with a 2x block and a sledge-hammer (photo bottom left, p. 57). The OSBfloor sheathing we use lies flat, and the tonguesslide easily into the grooves. When plywood isspecified, it's usually necessary to have an extracrew member stand on the seam to flatten thesheet. We adjust the joist that falls under the endof that sheet so that half or about in. of thejoist is left exposed. The outermost corner of thesheathing is then nailed to secure the joist in po-sition. After each course of sheathing is tackedin place in this manner and before the next

course is started, we hook a tape onto any ofthe secured joists and measure, adjust and nailthe rest of the joists at their proper 16-in. o.c.position with a single nail at the edge of thesheathing (photo right, p. 57).

We stagger the butt joints between sheets 4 ft.with each successive course. When the layoutapproaches an area where the joists overlap, weinstall 2x blocking to support the end of the

sheet as needed (photo left, facing page). After we've tacked the whole field of sheets in place,we snap lines to indicate joist locations, takingcare to shift our lines where the joists overlapor change direction (photo right, facing page).One crew member then finishes all the nailingso that he can keep track of what's been nailed.

Tying up loose ends W henever our sheath-ing runs by an opening such as the stair chase or the opening for the chimney, we either let asmall section of sheathing overhang or leave asmall uncovered area to begin the next sheet at

the edge of the opening. With the bulk of thefloor sheathed, we now turn to these details,trimming and filling in as needed.

Because the sheets of sheathing are in.wide, we end up with a 5-in. void at the end ofour 44-ft. house. Rather than sacrificing severalsheets of sheathing for their tongues, we cut upscrap pieces of sheathing and use them as fillers.The unsupported joint is not a concern becauseit will be covered by the 2x6 w alls above.

It's rare to have a floor this wide. Most of thehouses we do are less than 30 ft. wide, so thesheathing shortfall is usually 3 in. or less. If we

don't have enough scrap sheathing to use as afiller strip, we use 1x3 strapping or rip a 1x6ledger instead, which is cheap and easy to use.

The last step is straightening the rim joists thatwere left unnailed during the sheathing opera-tion (photo above left). Measuring in in. fromthe corners at the ends of the rim, we snap a ref-erence line on top of the sheathing. We nowmove the rim joist in or out every 4 ft. or so untilthe distance from our line to the outside edge ofthe rim measures in., and we drive a nail atthat point. After the edge is tacked straight, wenail it off and trim off any excess sheathing.

The second-story floor deck is built prettymuch the same way. However, one step that wetake just before lifting the bearing walls that willsupport the next floor is laying out for the joistson top of the top plate, which is quicker thandoing the layout from staging. Once the wallsare up, we start the process of installing rimsand joists all over again.

Rick Arnold and Mike Guertin are contributing editors toFine Homebuildingand residential- construction consultants and builders in East Greenwich, Rl. Photos by Roe A. Osborn.

Just say no

Here in the Northeast, whereconstruction quality is often judgedby how much wood you can packinto a house frame, omittingbridging is a controversial ch o ic eUnless we exceed the 6:1 (depth -tothickness) ratio in our joist materia(2x12) where the CABO coderequires blocking or bridgingbetween joists, we almost never install it.

To the best of our knowledge,bridging h as never been pro ved toadd strength to a floo r but it isalmost certain to add squeaks. Inthe past we tried gluing in solid

blocks, and for several years weinstalled steel bridging as analternative to blocking. We'd installthe steel bridging tighter than aguitar string only to re turn a year later and find it had loosened andwas causing squeaks. Even thoughwe use kiln-dried material, theseasonal changes in humidity causethe joists to shrink and swellenough to render any type of bridging worthless.

We can just about guarantee

squeak-free floor in our homesunless our clients or an architectinsists on blocking or bridging. Inthose cases we are inevitablycalled back a year later to fix floor squeaks. The remedy for thesqueaks usually involves removingany solid blocks or bridging thatdidn't have to be removed whenthe plumbers and HVAC installersdid their work.

Instead , -in; tongue-and-groove:Structural sheathing glued and

nailed to the joists is effective attransferring loads to adjacent joistswhich is what blocking andbridging are supposed to do. Asextra insurance, we install acontinuous 1x3 strap nailed to theunderside of the joists down theCenter of the span in basementto keep the joists from twisting. lfthe ceiling is to be finished) such aabove a living space, we install 1x3strapping 16.in. o.c. across thewhole ceilingR. A. and M.G.

to bridging