The long view: History of rain water penetration

{"version":"0.3.0","atoms":[],"cards":[],"markups":[["b"],["strong"],["sub"],["em"],["a",["href","http:\/\/www.integral-corp.com\/","target","_new"]]],"sections":[[1,"h2",[[0,[],0,"An historic view of rain water penetration strategies"]]],[1,"p",[[0,[],0,"Historically, there was\nno building science, no testing services, and no ASTM. Yet most buildings still\nworked in protecting the interior from rain water penetration. How was this so?"]]],[1,"p",[[0,[],0,"The strategies were\nsimple and generally consistent from one climate and culture to another. There\nwere no sophisticated multiple-layer drainage systems with well-developed\nflashing details."]]],[1,"p",[[0,[],0,"This Indonesian\nvernacular structure serves as a good example of a tropical design that works\nwell in a hot, humid and wet climate. So what are the strategies employed?"]]],[3,"ul",[[[0,[],0,"Steeply sloped roofs \u2013 using gravity to shed rain water off the building"]],[[0,[],0,"Projected eaves \u2013 diverts water away from the building and shelters the top of the walls"]],[[0,[],0,"The flush vertical walls quickly shed water"]],[[0,[],0,"Raised floors keep the floor dry"]]]],[1,"p",[[0,[0],1,"Thatch\nRoof"]]],[1,"p",[[0,[],0,"The roof of the\nstructure above is thatch; the photo to the right is a detail of a thatched\nroof. This is one of the most widely used historic roofing designs. So how does\na thatched roof work? Is it a mass barrier?"]]],[3,"ul",[[[0,[],0,"A thatched roof needs to be steep; at\nleast 45 degrees. It uses gravity to run water off"]],[[0,[],0,"The reeds are overlapping and all\ndirecting rain water down and away from the roof"]],[[0,[],0,"There are projected eaves directing\nwater away from the building"]],[[0,[],0,"The reeds are closed hollow tubes,\nwhich do not hold water; they do not get saturated or mushy"]],[[0,[],0,"\u001dThe reeds are tightly bundled and at\nleast 12\u201d thick with water penetration generally limited to the top one or two\ninches"]]]],[1,"p",[[0,[],0,"\n\n\n\n"]]],[1,"p",[[0,[],0,"\n\n\n\n"]]],[1,"h2",[[0,[],0,"Huts - An exploration in rain water penetration strategies"]]],[1,"p",[[0,[0],1,"Architect Designed\nBuildings \u2013 Historic"],[0,[],0,"\n\n\n\n\u0004"]]],[1,"p",[[0,[],0,"Even not so long ago\narchitects were designing buildings without much building science, limited\ntesting services, and limited ASTM. These buildings also generally worked."]]],[1,"p",[[0,[],0,"The key rain water\npenetration strategy of the opaque walls was utilizing a \u201cmass barrier\u201d design."]]],[1,"p",[[0,[0],1,"Historic Modern Buildings"]]],[1,"p",[[0,[],0,"Then buildings got\nlighter and thinner. Perfection was required. The rain water penetration\nstrategy is a face-sealed system. Face-sealed systems fail."]]],[1,"p",[[0,[],0,"Before we look at\ndifferent strategies to prevent rain water penetration we will take a quick\nlook at the forces that drive water through walls."]]],[1,"p",[[0,[0],1,"Forces Driving Rain Water\nthrough Walls"],[0,[],0," - "],[0,[0],1,"Vectors of multiple\nforces"]]],[1,"p",[[0,[],0,"Generally forces work\nin combination; there is not one single force driving rain water into\nbuildings."]]],[1,"p",[[0,[],0,"In the illustration\nthere is the downward force of gravity and an inward but slightly upwind force.\nThe result is a force with a in and down leg. While gravity is a constant at a\ngiven elevation the wind force is a variable."]]],[1,"p",[[0,[0],1,"Gravity"]]],[1,"p",[[0,[],0,"For vertical smooth\nwalls, gravity by itself is not a force driving water into the wall. There\nneeds to be some force driving water into the wall. But gravity adds a force\nvector that, in combination with other forces, can lead to rain water\npenetration."]]],[1,"p",[[0,[],0,"Good rain water\npenetration design uses gravity to divert rain water down and away from the\nbuilding."]]],[1,"p",[[0,[0],1,"Wind"]]],[1,"p",[[0,[],0,"Wind is not uniformly\napplied to surfaces and changes direction and changes the applied forces. Wind\nforces are in and out, up and down creating positive and negative forces."]]],[1,"p",[[0,[],0,"Geometry does play a\nsignificant factor. The pressures at the corners is greater than the middle of\nwall surfaces. One side can be under a high positive pressure and the opposite\nside under a negative pressure."]]],[1,"p",[[0,[1],1,"Surface\nTension"]]],[1,"p",[[0,[],0,"A contractive tendency of\nthe surface of a liquid that allows it to resist an external force; gravity and\npressure differences are such forces. The use of drips addresses this force."]]],[1,"p",[[0,[0],1,"Capillary Action"]]],[1,"p",[[0,[],0,"Capillary action\nresults from a combination of the surface tension of the water and the adhesive\nforces between the water and adjacent materials. It results in the ability of a\nliquid to flow in narrow spaces without the assistance of, and in opposition to\nexternal forces like gravity."]]],[1,"p",[[0,[],0,"Where tight channels\nare part of the design a capillary break solves the problem."]]],[1,"p",[[0,[0],1,"Pressure Differential"]]],[1,"p",[[0,[],0,"Pressure differential\nforces are primarily linked to wind load \u2013generally viewed when\naddressing multiple-element wall assemblies with a cavity. When the pressure\nwithin the cavity (P"],[0,[2],1,"c"],[0,[],0,") equals the pressure on the surface of the\ncladding from the outside (P"],[0,[2],1,"o"],[0,[],0,") then the force from the outside is\ncanceled out, and this prevents rain water penetration."]]],[1,"p",[[0,[0],1,"Diffusion"]]],[1,"p",[[0,[],0,"When water penetrates\ninto a material that has some porosity there is movement from a region of high\nconcentration of moisture to a region of low concentration."]]],[1,"p",[[0,[0],1,"Wall Assembly Strategies"],[0,[],0," - "],[0,[0],1,"Mass Walls"]]],[1,"p",[[0,[],0,"Rain water penetrates\nthe exterior of the wall due to porosity (low permeability is better). Movement\nis generally by diffusion. The wall has sufficient storage capacity and there\nis a short drying cycle, which dries out the wall between rain events."]]],[1,"p",[[0,[],0,"The thatched roof\nis such a system (roof rather than wall)."]]],[1,"p",[[0,[0],1,"Face Sealed Walls"]]],[1,"p",[[0,[],0,"Some have referred to\nthis wall as a perfect wall; but since design, materials and construction\ncannot assume perfection, this is not a recommended strategy."]]],[1,"p",[[0,[],0,"This wall would\nrequire perfect materials, in perfect assemblies with perfect joints between\ncomponents of the system and perfect joints at the interface of this system and\nadjacent systems."]]],[1,"p",[[0,[],0,"Good luck with\nthat!"]]],[1,"p",[[0,[0],1,"Cavity Walls (masonry,\nnon-vented)"]]],[1,"p",[[0,[],0,"A typical masonry\ncavity wall system consists of veneer brick, an air space, continuous\ninsulation, a control layer and a substrate system. In addition, there are\nties, anchors, flashings, weeps, etc."]]],[1,"p",[[0,[],0,"Water can penetrate\nthe veneer, and the moisture is generally absorbed or travels down the back\nface of the veneer within the cavity and directed back out of the wall at the\nflashing."]]],[1,"p",[[0,[0],1,"Drainage Plane \u2013 Stucco Wall"]]],[1,"p",[[0,[],0,"This wall assembly is\nsimilar to the masonry cavity wall assembly; stucco is the cladding rather than\nthe brick and a drainage mat replaces the air space."]]],[1,"p",[[0,[],0,"The drainage mat\ncaptures any moisture or water that penetrates the cladding, and it is directed\nto the bottom of the cavity where there is flashing and weeps directing the\nwater back out of the system. Drainage mats have a core, which permits the free\nflow of water and to each side of the core there are wicking membranes."]]],[1,"p",[[0,[],0,"\n\n\n\n\n"]]],[1,"p",[[0,[0],1,"Grilled \/ Lattice Cladding\n(almost a single element assembly)"],[0,[],0,"\n\n\n\n "]]],[1,"p",[[0,[],0,"Don\u2019t be fooled into thinking that all open-joint multiple element\nsystems are rain screens; some are barely multiple element systems at all."]]],[1,"p",[[0,[],0,"An open-joint cladding system that allows UV\npenetration and has a quasi-cavity is almost a face-sealed system in disguise."]]],[1,"p",[[0,[0],1,"Back-Ventilated Drained\nCavity Wall Assembly"]]],[1,"p",[[0,[],0,"In this assembly the\ncladding takes the brunt of exterior forces, provides UV protection to the\ncontrol layer, and has defined tight openings or vents. There is a cavity,\ncontinuous insulation, an air \/ water \/ (maybe vapor control) layer. Any\nmoisture is redirected back out of the wall system."]]],[1,"p",[[0,[0],1,"Drained and Back-Ventilated\n(Rain Screen?) Wall Cladding Assembly"]]],[1,"p",[[0,[],0,"This assembly is\ndistinguished from the above assembly by a cladding system (rain screen), which\nis designed to address all rain water penetration forces except those\nassociated with Pressure Differential."]]],[1,"p",[[0,[],0,"There is venting\nthrough the cladding to the cavity, but it is controlled. The air \/ vapor\ncontrol layer does not need to be a high performing water barrier such as\nwaterproofing."]]],[1,"p",[[0,[1],1,"Pressure Moderated\n(Equalized) Rain Screen Wall Cladding Assembly"]]],[1,"p",[[0,[],0,"The difference between this\nassembly and the assembly above is that the cavity is compartmentalized so the\npressure differential between the force on the face of the cavity and the force\nwithin the cavity is minimized. This prevents rain water penetration through\nthe cladding. This requires an analysis of how to compartmentalize the cladding\n(large compartment mid-wall and small compartments at the corners and edges)\nand calls for an analysis of sizing and distribution of vents."]]],[1,"p",[[0,[],0,"To develop a\nterminology specific to rain water penetration wall assemblies requires an\nunderstanding of the various forces that drive water into wall assemblies, the\nwall assembly strategies adopted to prevent rain water penetration, and the\nmaterials and system used."]]],[1,"p",[[0,[],0,"We are not assuming\nthat we have all the answers and we are not presenting a refined terminology\nthat we would want to impose upon others. But we are with you in exploring the\nissues and looking to work with attendees to help shape a terminology."]]],[1,"p",[[0,[1],1,"About the Author"]]],[1,"p",[[0,[3],1,"Micheal Lough is the principal and founder of "],[0,[4,3],2,"Integral Consulting"],[0,[3],1,", a consulting practice specializing in various services for owners, project management firms and architects including building enclosure consulting, peer reviews, property condition assessment, specifications, and building code and accessibility and code reviews."]]],[1,"p",[[0,[],0,"\n\n\n\n"]]],[1,"p",[[0,[],0,"\n\n\n\n\n"]]],[1,"p",[[0,[],0,"\n\n\n\n"]]],[1,"p",[[0,[],0,"\n\n\n\n\n"]]],[1,"p",[[0,[],0,"\n\n\n\n"]]],[1,"p",[[0,[],0,"\n\n\n\n"]]],[1,"p",[[0,[],0,"\n\n\n\n"]]],[1,"p",[[0,[],0,"\n\n\n\n"]]],[1,"p",[[0,[],0,"\n\n\n\n"]]],[1,"p",[[0,[],0,"\n\n\n\n"]]],[1,"p",[[0,[],0,"\n\n\n\n\n"]]],[1,"p",[[0,[],0,"\n\n\n\n"]]],[1,"p",[[0,[],0,"\n\n\n\n"]]],[1,"p",[[0,[],0,"\n\n\n\n\n"]]],[1,"p",[[0,[],0,"\n\n\n\n"]]],[1,"p",[[0,[],0,"\n\n\n\n"]]],[1,"p",[[0,[],0,"\n\n\n\n\n"]]],[1,"p",[[0,[],0,"\n\n\n\n"]]],[1,"p",[[0,[],0,"\n\n\n\n"]]],[1,"p",[[0,[],0,"\n\n\n\n"]]],[1,"p",[[0,[],0,"\n\n\n\n"]]],[1,"p",[[0,[],0,"\n\n\n\n"]]],[1,"p",[[0,[],0,"\n\n\n\n"]]],[1,"p",[[0,[],0,"\n\n\n\n"]]]]}