German Society for Wood Research (DGfH e.v.) Bayerstraße 57-59/V D München. Short Report

Transcription

1 Leipzig Institute fr Materials Research and Testing () Business Divisin IV Building Physics Hans-Weigel-Str. 2 b, D Leipzig Munich Technical University () Department f Civil Engineering and Surveying Chair f timber cnstructin and structural design Arcisstraße 21, D München German Sciety fr Wd Research (DGfH e.v.) Bayerstraße 57-59/V D München Shrt Reprt Experimental and numerical study n the hygrthermal behaviur f nnventilated wden flat rfs using eclgical prducts with a view t the develpment f damage-free and sustainable cnstructins This prject was supprted by German Sciety fr Wd Research (DGfH e.v.) by means f research prgram Zukunft Bau f German Federal Ministery f Transprt, Building and Urban develpment (BMVBS) and f Federal Office fr Building and Reginal Planning (BBR). Prject number: Z Prject perid: September April 2009 Authrs: Industry partners: Univ.-Prf. Dr.-Ing. Stefan Winter () Dipl.-Ing. Claudia Fülle () Dipl.-Ing. Nrman Werther () Leipzig, May 2009

2 Wden flat rfs - Shrt Reprt 2 1 Research Prject 1.1 Intrductin Flat rfs are actually strngly in demand in the industry and administratin building sectr, but als by private huse builders. Ventilated flat rf cnstructins cannt assure necessary ventilatin because f the marginal rf inclinatin. Mrever they are nt architecturally interesting n accunt f their height f cnstructin. German Standard (DIN ) demands fr nnventilated flat rf cnstructins either insulatin abve the sealing r a tight vapur barrier (s d = 100 m). Many examples f built flat rfs have shwn that cnstructins with tight vapur barriers can easily cause damages: Misture cming frm cnstructin prcess r entering by cnvectin cannt dry ut in summer thrugh the tight vapur barrier. A misture-variable diffusin-checking layer can shw cnsiderable advantages here. The cllectin f data and knwledge n the hygrthermal behaviur f different cnstructins f nnventilated wden flat rfs by systematic utdr experiments was therefre the key aim in the present research prject. On the basis f these experimental studies validatin f further numerical calculatins was carried ut. These further numerical calculatins were made in rder t find limits f the cnstructins and t evaluate bundary cnditins. Fllwing subjects have been discussed: Hw much can the usage f misture-variable vapur checks, riented strand bards and sealings with relatively lw vapur diffusin resistance help t avid damages? Which criteria have t be cmplied with when using eclgical insulatin materials such as cellulse r riented strand bards? Hw much des the sealing (clur f sealing, green rf, with gravel, shaded) have an influence ver the hygrthermal behaviur in the rf cnstructin? With the help f these data, sustainable and rugged cnstructins with satisfying level f reliability have been develped. Future damages caused by missing experiences and ut-dated standards can be avided. Besides, cmmercial lsses fr cnstructin cmpanies can be minimised. Furthermre, a study n built examples has been carried ut in rder t link the experimental study with practical experiences.

3 Wden flat rfs - Shrt Reprt Experimental study Test building in Leipzig The experimental study was carried in an utdr test building at, where different nnventilated wden flat rfs were built (figure 1). The rf cnstructins differed in the inside diffusin-checking layer, the insulatin material and the sealing (figure 2). The utilised flat rf had a surface f 8 x 5,5 m. The rf, which was inclined with 2, was brdered by an attic. In rder t avid shading, testing surface was always at 0,5 m frm the attic. There were 8 measuring fields (4 with black PVC sealing, 4 with green rf), each f them with a surface f 3 m². The measuring fields were separated frm each ther by partitin bards. Furthermre, there were 3 measuring fields (with pale PVC sealing, with gravel, shaded) in rder t Figure 1 Test building in Leipzig determine the influence f sealing layer. The interir rm was air-cnditined in rder t get rdinary usage cnditins. The fllwing 11 variants have been built: shaded Black PVC Black PVC Green rf, Green rf, sealing, sealing, cellulse, mineral wl, cellulse, mineral wl, OSB OSB OSB OSB With gravel Black PVC sealing, cellulse, misture-variable vapur check Black PVC sealing, mineral wl, misture-variable vapur check Green rf, cellulse, misture-variable vapur check Green rf, mineral wl, misture-variable vapur check Pale PVC sealing Figure 2 Test building in Leipzig, variants f rf cnstructin N

4 Wden flat rfs - Shrt Reprt Measurements The fllwing data were recrded in the test building: Outdr and indr climate Temperature and relative humidity f uter air Wind directin and wind velcity Vertical rain Glbal radiatin Temperature and relative humidity f internal air Hygrthermal cnditins in the rf cnstructin Temperature under the sealing Temperature and relative humidity in the critical sectin, between insulatin and OSB (upper planking) Misture cntent Misture cntent f timber frame and f OSB (upper planking) utside außen innen inside Temperature a) Außenlufttemperatur Outer air b) Oberfläche Surface f Abdichtung sealing c) Innenseite between insulatin äußere and OSB-Platte d) Raumlufttemperatur internal air rel. Relative Luftfeuchte humidity a) Außenluftfeuchte Outer air b) Innenseite between insulatin äußere and OSB-Platte c) Raumluftfeuchte Internal air Hlzfeuchte Misture cntent a) a) OSB-Platte OSB, middle Feldmitte f field b) b) OSB-Platte OSB, brder am f Sparren field c) c) Sparren Rafter außen Klima Climate Glbalstrahlung radiatin Nrmalregen Vertical rain Windgeschwindigkeit directin and wind velcity Figure 3 Placement f measuring technique Evaluatin criteria Damages will ccur when wden building parts r derived timber prducts, such as riented strand bards (OSB), shw high misture cntents ver lnger perids and when the capability f drying ut in summer is t lw t lead away arisen misture. In the present research prject, requirements and evaluatin criteria have been derived frm the applicatin ranges f the derived timber prducts and frm requests in rder t avid the grwth f muld fungus. Critical building parts in the examined rf cnstructins are the upper riented strand bards (OSB) and the wden rafters. The misture cntent in the upper riented strand bards must nt exceed the limiting value f 18 M-% ver a lnger perid. The misture cntent f the rafters must nt exceed the limiting value f 20 M-% ver a lnger perid. In rder t avid the grwth f muld fungus, relative humidity in the critical sectin, between riented strand bards (OSB) and insulatin, must nt exceed the limiting value f 80 % ver a lnger perid.

5 Wden flat rfs - Shrt Reprt 5 2 Measurement results frm test building 2.1 Flat rf cnstructins with black PVC sealing Figure 3 Relative humidity in the critical sectin (between insulatin and upper OSB), measured mean daily values Figure 4 Misture cntent in the upper OSB, measured mean daily values Figure 5 Misture cntent in the rafters, measured mean daily values

6 Wden flat rfs - Shrt Reprt Flat rf cnstructins with green rf Figure 6 Relative humidity in the critical sectin (between insulatin and upper OSB), measured mean daily values Figure 7 Misture cntent in the upper OSB, measured mean daily values Figure 8 Misture cntent in the rafters, measured mean daily values

7 Wden flat rfs - Shrt Reprt 7 3 Hygrthermal calculatins Numerical simulatins fr all cnstructin variants were carried ut with a numerical prgram fr cupled heat and misture transfer (WUFI). Therefre, measured data f utdr and indr climate were used. Measured data and results f numerical simulatin agreed very well with each ther. The fllwing figures shw, as an example, a cmparisn f measured data and calculatin results fr variant 1.2 (black PVC sealing - OSB - cellulse - misture-variable vapur check): Figure 9 Temperature in the critical sectin (between insulatin and OSB) in var. 1.2 Figure 10 Relative humidity in the critical sectin (between insulatin and OSB) in var. 1.2 On the basis f validated material data, further hygrthermal simulatins (parameter studies) were carried ut. Examined cases were: Variatin f uter climate (calculatin fr climate Hlzkirchen 1991 ) Variatin f inside climate (simulatin f higher internal relative humidity because f e.g. making flr ) Cnsideratin f cnvective entry f misture (250 g/(m² winter)) Variatin f sealing (calculatin fr pale PVC sealing and diffusin resistant sealing such as bitumen) Simulatin f shading by adjacent buildings Simulatin f superstructures (e.g. phtvltaics)

8 Wden flat rfs - Shrt Reprt 8 4 Cnclusin The present studies in the test building in Leipzig have shwn that nnventilated wden flat rf cnstructins are able t perfrm withut damages when cnsidering certain cnstructive bundary cnditins. Further knwledge n limits and usage cnditins f the rf cnstructins culd be derived frm extensive numerical simulatins. Studies n existing buildings with wden flat rfs supplement the measurements in the test building and the parameter studies. The examined 8 variants differed largely cncerning their hygrthermal behaviur. The fllwing cnstructins perated successfully and can therefre be recmmended: Variant 1.2 Variant 1.1 Variant 2.2 Variant 3.2 Black PVC sealing - OSB - cellulse - misture-variable vapur check Black PVC sealing - OSB - cellulse - OSB Black PVC sealing - OSB - mineral wl - misture-variable vapur check Green rf - OSB - cellulse - misture-variable vapur check In singular cases, further studies must be carried ut fr: Variant 2.1 Black PVC sealing - OSB - mineral wl - OSB The fllwing variants cannt be recmmended: Variant 3.1 Green rf - OSB - cellulse - OSB Variant 4.1 Green rf - OSB - mineral wl - OSB Variant 4.2 Green rf - OSB - mineral wl - misture-variable vapur check The fllwing key results were gained: A srptive insulatin material such as cellulse is able t buffer misture and therefre t cntribute t hygric stress relief which can be caused by misture cming frm cnstructin prcess r entering by cnvectin. Therefre the srptive insulatin material must be preferred t e.g. mineral wl. A misture-variable vapur check is advantageus cmpared t an riented strand bard because f its wider range f water vapur diffusin resistance. The usage f a black PVC sealing with a relatively lw water vapur diffusin resistance (s d ~ 20 m) ffers key benefits cncerning hygrthermal behaviur in cmparisn t the usage f pale PVC sealing r relatively tight sealings such as bitumen (s d ~ 300 m). Nnventilated wden flat rfs remain sensitive cnstructins and demand higher diligence and quality cntrl frm planning t cnstructin. Hwever: If ne carries ut a crrect, airtight cnstructin, chses suitable materials fr insulatin, internal diffusin-checking layer and sealing, and cnsiders basic demands n bundary cnditins, nnventilated wden flat rfs perfrm very well and perate withut damages.