38 research outputs found
When the safest solution is unacceptable
No full textBuilding physical problems are often the reason for renovations of dwellings. Although methods to rectify the problems are available, the building owners are often unwilling to accept the safest solutions for economical reasons. Practitioners are therefore forced to develop alternative solutions, which are cheaper but only lessens the problem or are less robust in more extreme situations. When alternative renovation solutions are considered, building simulation tools are often used to predict how the different solutions will work. However, depending on the chosen conditions, simulations can be manipulated to show, that almost any solution will work. This mimics the real world; in dwellings one apartment can have a serious mould problem, while another similar apartment is dry, warm and healthy. The reason is often different user behaviour. The dilemma of the practitioner is that some solutions will be sufficient for many users, but some users need safer solutions, which often are more expensive. It is therefore important to explain to the building owner that with the safe solution user behaviour become less important; he buys robustness. Therefore, when new solutions for renovation are considered, the degree of robustness must be considered, and then it is up to the building owner to decide which solution he can afford. The method emphasizes the importance of educating building users, and the safest solution can be seen as insurance, if the education fails. The paper presents examples of renovations based on building physical problems where alternative, less robust solutions have been chosen, based on simulations and tested on pilot projects. Ways to present robustness and to choose pilot projects are also shown.Presenters:
name: Eva Birgit Møller
affiliation: (Birch & Krogboe A/S)
email: [email protected]
Parameter study of wooden beam ends in combination with interior isolated masonry facades.
No full textMoisture conditions highly insulated, ventilated roofs: parametric study - hygrothermal calculations
No full textDe sidste 10-års stramninger i Bygningsreglementet med henblik på at reducere energiforbruget ibygninger, har bl.a. inkluderet krav om begrænsning af varmetabet gennem klimaskærmen. Deskærpede krav har således medført, at konstruktionerne skal varmeisoleres mere. Specielt i tagetanvendes store isoleringstykkelser, da det i de fleste tilfælde er mest fordelagtigt sammenlignetmed isolering af klimaskærmens øvrige bygningsdele. I højisolerede ventilerede tage er varmetabetmindre og tagrum og ventilationsspalte koldere end tidligere, og mængden af fugt, der kanoptages af ventilationsluften, er dermed mindre. Dette medfører øget risiko for fugtproblemer itagkonstruktionen.Masterprojektets har til formål at undersøge fugtsikkerheden i højisolerede, ventilerede tage medtrækonstruktion, der opfylder kravene i Bygningsreglementet og anvisninger i det alment tekniskefælleseje. Det undersøges hvordan fugtproblemer i højisolerede, ventilerede tagkonstruktionerundgås inden for rammerne af gældende regler.Først sammenfattes gældende danske regler for ventilerede tage indenfor området fugt og fugtsikkerhedsamt udvalgte relaterede studier. Undersøgelsen af fugtforholdene i højisolerede, ventileredetage er udført som parameterstudie med en reference konstruktion for både et paralleltagog tagrum. Parametervariationerne vedrører forskellige konstruktionsopbygninger og materialer,og andre forhold i konstruktionen, samt randbetingelser ved inde- og udeklima. Beregningerne erudført ved brug af computerprogrammerne WUFI Pro 5.3 og BSim.Det ikke er muligt at udelukke risikoen for vækst at skimmelsvamp i naturligt ventilerede tage,hvor de ydre dele af tagkonstruktionen udsættes for danske udeklimaforhold. Risikoen for skimmelsvampevækstkan dog begrænses ved korrekt projektering og udførelse af de ventilerede tage,hvor række faktorer har indvirkning på fugtforholdene i tagkonstruktionerne, og derfor skal indgåovervejelserne for at opnå bedre fugtsikkerhed. De væsentligste faktorer er oplistet nedenfor:• En øget isoleringstykkelse vil øge risikoen for vækst af skimmelsvamp i tagkonstruktionerne,men så længe ikke andre faktorer præger fugtforholdene i tagkonstruktionen negativt,vil den øgede risiko for skimmelsvampevækst være begrænset. Det giver alene pådenne baggrund ikke anledning til ændringer af ventilerede tage.• Luftskiftet i ventilationsspalten skal være tilpas stort til at fjerne den mængde fugt, deruundgåeligt vil blive tilført tagkonstruktionen. Er luftskiftet for lavt vil dette ikke ske, ogrisikoen for fugtproblemer i tagkonstruktionen bliver stor. Luftskiftet må dog ikke væreså højt, at det sænker temperaturen i konstruktionen, da det vil øge den relative fugtighed,og dermed risikoen for skimmelsvampevækst.• Tagkonstruktioner af træ er følsomme overfor enhver form for lækager, utætheder i undertagetsom medfører vandindtængen, utætheder i dampspærren og byggefugt.Resultaterne er baseret på 75 fugtberegninger i ventilerede paralleltage og tagrum.The last ten years of tightening of the Building Code with the purpose of reducing energy consumptionin buildings have included requirements for the reduction of heat loss through thethermal envelope. The higher demands have led to increased thermal insulation of buildings. It ismost often seen as favorable to apply very thick layers of insulation to roofs as compared to otherparts of the building envelope. In highly insulated, ventilated roofs the thermal loss is reducedand attics and ventilated cavities are consequently colder than before. This reduces the amount ofhumidity the ventilation air can thus absorb, leading to increased risk of moisture build-up in theroof structure.This master project aims at investigating the moisture safety in highly insulated, ventilated roofswith wooden structure that comply with requirements in the Building Code and technical instructionsfrom generally recognized organizations and institutions.Current Danish regulations and related studies regarding moisture and moisture safety in ventilatedroofs are summed up. The investigation of moisture conditions in highly insulated, ventilatedroofs is done as a parameter study with a reference construction for both a cold roof and a coldattic. The parameter variations regard different forms of construction and different materials aswell as other aspects of the structure, and also the edge conditions concerning indoor climate andoutdoor climate. For the calculations the hygrothermal calculation tools WUFI Pro 5.3 and BSimis used.There will always be a risk of mould in outdoor-air ventilated roofs subject to Danish climateconditions. However, this risk can be limited through correct project design and execution of aventilated roof. A range of factors influence the moisture conditions and these must thereforeenter into the work on moisture risk. The most important factors are listed below:• Increased insulation thickness increase the risk of mould in the roof constructions, but solong as no other factors influence the moisture conditions in the roof construction in anegative way the increased risk will be limited. On this background alone this does notlead to alterations of ventilated roofs.• The air change in the ventilated cavity must be sufficient to eliminate the humidity whichwill inevitably be fed to the roof construction. An insufficient air change will not do thisand the risk of moisture problems will increase. However, the air change must not be sohigh that it decreases the temperature in the roof construction since this would increasethe relative humidity and thus also the risk of mould.• Wooden roof constructions are sensitive to any type of leakage, leaks in the roof underlayleading to water ingress, leaks in the vapor barrier and humidity in the structure stemmingfrom the building process.The results are based on 75 hygrothermal calculations on ventilated cold roofs and cold attics
The moisture hood in praxis
No full textVed fugtmålinger på eksisterende konstruktioner findes der umiddelbart ingen enkle og billige løsninger til direkte bestemmelse af fugtindholdet. De kendte løsninger har signifikante fejlkilder, og det er ikke altid helt entydigt, hvor højt et fugtindhold, en konstruktion fremstår med.Derfor er der udviklet en fugthætte, der ved hjælp af et lille lukket kammer, der påklæbes en konstruktion, kan bestemme porefugtindholdet i konstruktionens overflade. Løsningen udnytter, at luften i hætten inden for et vist tidsinterval vil indstille sig i en ligevægt med porefugtindholdet.Formålet med dette projekt var at teste fugthætten af i praksis på eksisterende konstruktioner. Dette er hovedsageligt sket på ubehandlede betonkonstruktioner med forskellige variationer af opfugtning. Dertil var formålet også, at vurdere ”hukommelsen” af forskellige bygningsmaterialer samt at diskutere forhold som f.eks. overfladebehandlinger og diffusionstæthed.I projektet er det vist, at stigningen af fugtindholdet i fugthætten efter opsætning på en konstruktion er forholdsvis forskelligt, hvilket i nogen grad afhænger af konstruktionens overfladebehandling. Derfor har det ikke været muligt at opstille en algoritme til bestemmelse af fugtindholdet i konstruktionen ud fra målinger inden for de første timer. Der har dog vist sig en sammenhæng mellem udviklingen i målingerne inden for de første 2 timer og så det endelige fugtindhold i fugthætten når der har indstillet sig en ligevægt. Denne sammenhæng er forklaret via et fremskrivningsskema, som er opstillet ud fra resultaterne i undersøgelserne. Udtørringsforsøg er benyttet til at illustrere forskellen mellem de forskellige materialers ”hukommelse”, hvor det viste sig, at mursten har en kortere udtørringstid end betonfliser. Resultaterne har dog også vist, at gipspladerne, der er benyttet i disse forsøg har haft en længere udtørringstid end murstenene, men dette skyldes det betydeligt højere indledende fugtindhold inden udtørringen i gipsen end i murstenene. Endeligt er det vurderet, at diffusionstætheden af fugthætten spiller en ringe betydning i forhold til de resterende fejlkilder, såsom overfladens tilstand samt tilslutningsevnen mellem konstruktionerne og selve fugthætten. Alt i alt er fugthætten et interessant og bestemt brugbart supplement til eksisterende anerkendte målemetoder, om end der fortsat er behov for videreudvikling og yderligere afprøvning. Mulighederne for praksis anvendelse vurderes særdeles gode, hvis forhold omkring specielt intern lagring løses.There are numerous methods for measuring the moisture content in buildings and building materials. However, there are no easy and cheap methods for direct measurements of the moisture content. Furthermore the existing methods have various significant sources of error with respect to the actual determination of moisture content in a given material. To meet this need for moisture measuring, the moisture hood has been developed. In general, it consists of an enclosed chamber, which is attached to a building material. When equilibrium between the moisture content in the material pores and the moisture content in the chamber is obtained and the moisture content in the pores can be measured.The main focus in this project was to test the moisture hoods practical application on in existing buildings. This has mainly been on raw concrete walls with various amounts of moisture contents. Furthermore, it was the objective that the “memory” of different building materials should be investigated. Finally different wall coverings and water vapour resistance is discussed.In this study it is shown that the increase in moisture content in the moisture hood when applied to different building material is rather diverse, mainly due to the condition of the surface. Due to these differences, it has not been possible to complete an algorithm for determination of the final moisture content based on short term measurements. However, a correlation between the first measurement and measurements after 2 hours have shown, that it is possible way to predict the moisture content in the material. This has resulted in a prediction scheme, which is presented in this report.To illustrate the differences in “memory” as a function of building material, desiccation experiments have been performed. Here it is seen, that bricks have a shorter drying time than concrete tiles. The results also show, that gypsum boards have a longer drying time than bricks. This however, is caused by a much higher initial moisture content in the gypsum board study when compared to the study with bricks and concrete tiles.Finally it is assessed, that the water vapour resistance of the moisture hood is of subordinate importance when compared to other error sources, such as the condition of the surface and the adhesion between the building material and the moisture hood.In conclusion, the moisture hood is a fully applicable addition to existing moisture measurement methods, however, further experiments and testing is needed. At present the possibilities for use of the moisture hood needs to be complemented, especially with loggers with internal storage for optimal use
